WO1997037756A1

WO1997037756A1 - An improved clean, stiff, washable, compact adsorbent filter assembly

Info

Publication number: WO1997037756A1
Application number: PCT/US1997/003757
Authority: WO
Inventors: Edwin G. Dauber; Michael F. Stiles; Michael S. Winterling
Original assignee: W.L. Gore & Associates, Inc.
Priority date: 1996-04-08
Filing date: 1997-03-11
Publication date: 1997-10-16
Also published as: AU2320997A

Abstract

An improved clean, stiff, washable, compact adsorbent filter assembly is provided for selectively adsorbing contaminants from an enclosure. The filter assembly comprises a sorbent core including contaminant adsorbing material therein, a filter layer, and a film layer wherein the sorbent core is encapsulated by the film layer and filter layer. Other layers such as a filter support layer and one or two low melt bonding layers may be added to the film layer. The filter assembly may also comprise an indicator chemical to indicate sorbent saturation. The filter assembly may also function to channel air into a particulate filter to maximize adsorbent effectiveness and recirculation filter effectiveness. The filter assembly is particularly suitable for use in a computer disk drive or similar enclosure susceptible to outgassing contamination. The filter assembly can be mounted by a variety of means including but not limited to a press fitting between 'C' channels, fastening in place with screws, or welding into place by means of a thermoplastic or thermoset adhesive.

Description

TITLE OF THE INVENTION

AN IMPROVED CLEAN, STIFF, WASHABLE, COMPACT ADSORBENT

FILTER ASSEMBLY

FIELD OF THE INVENTION

The present invention generally relates to devices for filtering or removing contaminants from a confined environment, such as gaseous contaminants in electronic or optical assemblies (e.g., computer disk drives). More particularly, the present invention provides an improved clean, stiff, washable, compact adsorbent filter assembly for use in such environments.

BACKGROUND OF THE INVENTION

Many enclosures that contain sensitive instrumentation must maintain very clean environments in order to operate properly. Examples of such enclosures include: enclosures with sensitive optical surfaces or electronic connections that are sensitive to particulates and gaseous contaminants which can interfere with mechanical or electrical operation; data recording devices, such as computer hard disk drives that are sensitive to particles, organic vapors, and corrosive vapors; and electronic control boxes such as those used in automobiles that are sensitive to moisture buildup and corrosion, as well as contamination from both inside and outside the enclosures. In computer hard drives, for example, damage may result from external contaminates as well as out-gassing from internal components.

One serious contamination-related failure mechanism in computer disk drives is static friction or "stiction." Stiction is the adhesion of a drive head to a disk while the disk is not moving. Newer high density disks are more sensitive to contamination caused stiction because they are smoother and contain only thin layers of lubricants. Contaminants on the disk change the surface energy and the adhesive forces between the disk and the head, which causes stiction. Also, vapors that condense in the gap between the head and disk can cause stiction. Further exacerbating these effects, new disk drives have smaller, low energy motors with lower torque. Additionally, disk drives must be protected against a large number of contaminants in the surrounding environment This protection is important for drives used in small to medium sized computer systems . hιch may not ' e used in a typical data processing environment This protection is particularly important in drives that are removable and transportable to any environment, such as disk drives that are used in Personal Memory Card International Association (PCMCIA) slots

Sorbent filters are useful in some applications in controlling contamination Sorbent filters must keep the enclosures free of contamination from both internal and external sources In addition to providing cleaner environments, filters must be made smaller to fit into small enclosures Space constraints exist, for example, in modern electronic components like computer disk drives Today PCMCIA computer disk drives have up to 240 MB of storage capacity and are only approximately 5 cm wide and 7 5 cm long Current production Type 3 PCMCIA drives have a maximum thickness of 10 5 mm Extremely compact Type 2 drives, which have a maximum thickness of 5 mm, and Type 1 drives, which have a maxtmum thickness of 3 3 mm, are planned for the near future

Sorbent breather filters used to keep particulates and vapors from entering enclosures are well known These can be made by filling a cartridge of polycarbonate, acrylonitnle butadiene styrene (ABS), or a similar material, with sorbent and securing filter media on both ends of the cartridge Examples of such filters are described in United States Patent Nos 4,863,499, 5,030,260, 5 124,856, and 5,417,743 Such known filters are not believed suitable for recent more demanding applications For instance, many of these kinds of filters present their own contamination risks, such as outgassmg from adhesives or chemicals, or particulation Further, in order to supply adequate quantities of sorbent matenals, most existing breather filters are too large to fit within increasingly smaller electronic components

A smaller compact adsorbent breather filter with the diffusion tube incorporated into the adhesive structure of the filter is also taught by United

States Patent No 5,417,743 This is an improved adsorbent breather filter with sufficient carbon to control acid gasses coming into the enclosure from the outside, but typically will not contain enough carbon to adsorb all the contaminants outgassmg from components within the enclosure or, in this case computer disk drive In a distinctly different use, U S Patent No 4,208 194 discloses a personal monitoring device that collects chemicals for testing The collecting layer is comprised of a porous polytetrafluoroethylene (PTFE; sheet containing a particulate sorbent Again, the collecting layer of this device may particulate and is not designed for use in small enclosures

A commercially successful "tube" filter is disclosed in U S Patent No 4,830,643 This patent teaches a sorbent filter having a powdered sorbent encapsulated in an outer expanded PTFE tube This tube filter is manufactured by W L Gore & Associates, Inc , of Elkton, Maryland, and is commercially available under the trademark GORE-SORBER® GORE-SORBER is a registered trademark of W L Gore & Associates, Inc While this apparatus is highly effective, the filter is currently available only in large and medium sizes (e g , minimum filter volumes of about 3 cc) In its present form, this filter is incapable of fully addressing growing needs for even smaller and more compact sorbent filters containing a high sorbent density

Sorbent filter manufacturers have encountered several obstacles in producing very small tube sorbent filters First, as tube size (diameter) decreases, filling the tube with sorbent powder becomes more difficult This problem is compounded by the common use of larger granular sorbent powders to avoid "dusting" contamination Second, as tube size decreases, it is more difficult to fill the tube filters without having the powder settle on the external tube surfaces and the seal areas The powder on the outside tube can contaminate the devices near the tube and also prevent the outer tube from sealing, which may also present dusting problems through leakage Third, as diameters are reduced, the ratio of the volume occupied by the sorbent matenal to the volume occupied by the sorbent filter assembly substantially and disproportionately decreases This disproportional volume decrease occurs because the volume occupied by the tubing wall thickness and the volume consumed by the crimping of the tube ends becomes a larger percentage of the total tube filter volume. Using a thinner tubing thickness could increase sorbent volume, but this increases tube filling difficulties and makes seal formation more difficult

Adsorbent pouches or adsorbent contained within two filter layers, such as two PTFE membrane laminates, are alternatives to the aforementioned sorbent filled tube, but such assemblies have the same restrictions as the tube filter Additionally, the laminates are typically weaker than the tubing, dusting often occurs on four sides instead of one and seams and seals are typically weaker

Alternatives to adsorbent breather filters are adsorbent "peel and stick" assemblies that contain an adsorbent between layers of a filter material and pressure sensitive adhesive that is used to mount the adsorbent to the enclosure interior These assemblies, however, place the adhesive inside the enclosure where outgassmg from pressure sensitive adhesives can tend to reduce the carbon capacity and escape from the assembly and be a source of vapor contamination into the enclosure

Another sorbent filter commercially available from W L Gore & Associates, Inc , comprises a composite sorbent-filled PTFE planar core which is laminated on its top and bottom surfaces with a porous expanded PTFE membrane This filter fits into slots in an enclosure inteπor The sorbent-filled PTFE core can be filled with various sorbent materials selected to adsorb hydrocarbons, moisture, out-gassed plasticizers, and corrosives, for example Although this sorbent assembly provides a low profile compact sorbent assembly, the unsealed sides of this device may not provide adequate protection from shedding of sorbent material particles Similar small filters with an adsorbent filled PTFE core and PTFE wrapped or extruded over the core are also available from W L Gore & Associates, Inc , but these filters are typically not stiff, and, therefore, more concern in design and application of these adsorbent filters must be taken Additionally, adsorbent recirculation filters are available for computer disk drives Small amounts of adsorbent are included within such filters to remove gasses and particulates from air that is recirculated through these filters by the spinning of the computer disks A shortcoming of these filters is that the addition of adsorbent to such filters increases the resistance to airflow through these filters, and thereby diminishes such filters' particulate clean up capability since more air bypasses these filters then flows therethrough

Additionally, it is difficult to contain the carbon in such a low efficiency, high air flow filter to prevent it from being a particulate source Also, the adsorbent content of such filters is typically low, particularly in smaller dimensioned filters The foregoing illustrates limitations known to exist in present adsorbent filter assemblies Thus it is apparent that it would be advantageous to provide an improved adsorbent filter assembly directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more f y disclosed hereinafter.

SUMMARY OF THE PRESENT INVENTION

The present invention advances the art of adsorbent filter assemblies beyond which is known to date. In one aspect of the present invention, a clean, stiff, washable, compact adsorbent filter assembly is provided for the reduction of vapor phased contamination in an enclosed area. In one embodiment of the present invention, a sorbent core (also referred to as an adsorbent core) contains an adsorbing material, a first film layer and a filtering layer such that the sorbent core is completely encapsulated between the film layer and the filtering layer. The film and filtering layers are sealed together around a perimeter of the filter assembly. A mounting hole or crosscut may be provided to facilitate mounting the filter assembly. An indicator material may be provided within the sorbent core to determine the level of saturation of the sorbent by visually inspecting the sorbent core through a transparent film layer. The filter layer can be hydrophobic such that the filter can be washed without extracting valuable water soluble salts used for chemisorption of acid vapors, or without fear of the transport of ions within the inner core to the filter surface. The filter can also contain one or two layers of hot melt adhesive to facilitate manufacture of the filter and/or adhereing the filter to the housing.

It is a purpose of the present invention to provide an improved clean, stiff, washable, and compact sorbent filter that effectively removes contaminants from an enclosed environment while occupying minimal space. It is another purpose of the present invention to provide an adsorbent assembly that can be mounted to provide an air directed chute to direct air into a recirculation filter and thereby set the adsorbent alongside a highly mixed active air stream.

Another purpose of the present invention is to provide a sorbent filter that can be die cut into any convenient shape, and can be cleansed such that surface contaminants and ions can be washed without extracting water soluble chemisorbents from the internal adsorbent mix and without transporting contaminating ions from the adsorbent back to the surface of the filter. It is an additional purpose of the present invention to provide a sorbent filter that is non-out-gassing and non-particulating

It is an additional purpose of the present invention to prov de a sorbent filter that is free of pressure sensitive adhesives Still another purpose of the present invention is to provide a sorbent filter that is easily made, readily handled, and easily installed that can also include indicators to show saturation in certain embodiments

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of a preferred embodiment of the invention, will be better understood when read in conjunction with the appended drawings For purposes of illustrating the invention, there is shown in the drawings an embodiment which is presently preferred It should be understood, however, that the invention is not limited to the precise arrangement and instrumentality shown In the drawings

Figure 1A is a top view of one embodiment of the sorbent filter assembly of the present invention, wherein a sorbent core is sealed between a film layer and a filter layer, Figure 1B is a side view of the embodiment shown in Figure 1A,

Figure 2 is a side view of an alternate embodiment of the present invention, wherein the film layer is coated with a layer of meltable adhesive that melts at a lower temperature than the film layer to aid in manufacturabi ty,

Figure 3 is a top view of an alternate embodiment of the present invention which includes a mounting hole,

Figure 4 is a top view of an alternate embodiment of the present invention wherein mounting cross haired slits are provided for both ends of the assembly to provide additional mounting flexibility,

Figure 5 is a side view of an alternate embodiment of the present invention showing a support layer added to the filter layer to aid in manufacturabihty,

Figure 6 is an environmental view of the sorbent filter assembly of the present invention mounted within a disk dπve assembly, such that the filter directs the natural air flow generated by the rotating disks into the path of a particulate recirculating filter, thereby placing the adsorbent alongside the highly mixed, turbulent air flow path to increase adsorption rates,

Figure 7 is a top ^{ψ •} . of the sorbent filter assembly of the Dresent invention mounted into "C" channels within a computer disk drive, similarly directing aπ air path into a particulate recirculation filter,

Figure 8 is a top view of the sorbent filter assembly of the present invention mounted into a drive under a clean tape seal, the mount facilitating visual inspection of a chemical indicator indicating a level of saturation of contaminants within the adsorbent material, and Figure 9 is a side view of an alternate embodiment of the present invention wherein the film layer is coated with a second layer of meltable adhesive that can be used to mount the filter directly to the housing

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein similar reference characters designate corresponding parts throughout the several views, the sorbent filter assembly of the present invention is generally illustrated at 15 in the Figures As shown in Figures 1A and 1B, the sorbent filter assembly 15 of the present invention comprises a sorbent core 12 sealed between a filter layer 10 and a film layer 14, with the sealed area designated area 22

The filter layer 10 may comprise any porous material that allows vapor contaminants to diffuse through it to the sorbent core 12 The filter layer 10 also keeps the sorbent material within the filter assembly 15 A hydrophobic filter layer 10 allows the filter assembly 15 to be washed in deionized (Dl) water to remove surface particulates and ions without extracting any water soluble chemical chemisorption treatments in the sorbent core and without allowing water transport of any ions from the sorbent core to the filter surface Suitable filter layer materials may include, but are not limited to, polymeric non-shedding filter media or laminated filter media, a porous membrane of polypropylene, polyethylene, nylon, composites of polycarbonate and polyester, mixed cellulose esters, cellulose triacetate or laminates of the foregoing, for example A preferred filter layer 10 for use in the present invention comprises a membrane of porous expanded polytetrafluoroethylene (PTFE) As the term is used herein porous polytetrafluoroethylene (PTFE) shall mean a membrane which may be prepared by any number of known processes, for example by stretching or drawing processes, by papermaking processes by processes in which filler materials are incorporated with the PTFE resir crd wmch are subsequently removed to leave a porous structure or by powder sintering processes Preferably, the porous polytetrafluoroethylene membrane is porous expanded polytetrafluoroethylene membrane having a microstructure of interconnected nodes and fibrils, as described in U S Patent Nos 3 953,566, 4,187,390, and 4,110,392, which are incorporated herein by reference, and which fully describe the preferred material and processes for making them The porous polytetrafluoroethylene membrane may have a thickness in a range from about 3 to about 1 ,000 micrometers, preferably in a range of from about 5 to about 100 micrometers, and a pore volume in a range from about 20 to about 98 percent Additionally, the filter layer 10 may be comprised of a PTFE membrane that is filled with a thermoplastic or thermoset material to ease welding or to facilitate attaching the filter layer 10 to the film layer 14 Such filled PTFE membranes are disclosed in U S Patent 4,732,626 and PCT Application PCT/UK91/00661 which are both incorporated by reference

A most preferred filter layer 10 is a porous PTFE membrane filled with a thermoplastic perfluroalkyl copolymer (PFA) The PFA is particularly suitable since it is inert, facilitates a good seal to the film layer 14, withstands reasonably high temperatures, and is non-outgassing A PFA filled porous PTFE membrane is also a hydrophobic membrane that allows washing of the filter in deionized water (Dl water), without extracting water soluble salts or chemisorbent treatments from the inner core, or allowing water transport of ions from the inner core to the surface of the filter

The sorbent core 12 may comprise any number of materials which may range from loosely packed particles to filled, or highly filled porous materials, for example As the terms "sorbent," "adsorbent," and "sorbing" are used herein, they are intended to encompass any material that removes contaminants from a surrounding environment, whether through a process of absorbing, adsorbing, or otherwise A core formed of loosely packed particles preferably contains a binder which holds the particles together Suitable binders include, but are not limited to, fluorinated ethylene propylene (FEP), polyvinyldiene fluoride (PVDF), acrylics or other conventional binders In addition, the sorbent core 12 may comprise one or more layers of an adsorbent or adsorbent filled material, such as a scaffold of a porous polymeric material, such as polyethylene for example, in which void spaces are filled with a sorbent Other possible constructions of the sorbent core 12 include sorbent impregnated woven or non-woven materials, such as cellulose or polymeric non-woven materials, which may include latex or other binders, as well as porous castings of sorbents and fillers that are polymeric or ceramic The sorbent core may include a single particular sorbent, or may include a mixture of different types of sorbents, the selection of which is dependent on the specific application The core can also be a woven or non-woven fabπc of carbonized material, such as an activated carbon fabric product sold by American Kynol, Inc , and manufactured by Kynol Corp in Japan.

A preferred embodiment of the sorbent core 12 utilizes a sorbent filled PTFE sheet wherein the sorbent particles are entrapped within a regular shaped PTFE structure, as taught by U.S. Patent No. 4,985,296, incorporated by reference Ideally, particles are packed in a multi-modal (e.g., bi-modal or tπ-modal) manner, with particles of different sizes interspersed around one another to fill as much of the available void space between particles as is possible to maximize the amount of active material contained in the sorbent core 12 Also, multi-modal packing permits a number of sorbents to be filled into a single sorbent core 12.

By using PTFE as a binder material for the sorbent core 12, a number of additional advantages are provided. PTFE is a non-linting, non-out-gassing inert binder that effectively reduces dusting of sorbent material during the manufacture and the life of the filter Additionally, processing advantages of this material include the ability to make a relatively thin, highly loaded material which can be produced in a wide sheet and then cut (or cut and folded) into desired final widths. In this manner, thin cores can be produced for very low profile sorbent filters. Additionally, a sorbent filled PTFE core has the capacity to achieve high sorbent loading densities. By controlling the sorbent particle sizes and by compressing the extruded sorbent filled PTFE core, very high density sorbent loadings can be achieved. The PTFE structure still allows vapors to penetrate even very densely packed formulations.

Examples of sorbent material that may be contained within the sorbent core 12 may include, but are not limited to physisorbents (e.g , silica gel, activated carbon, activated alumina, or molecular sieves), chemisorbents (e g , potassium permaganate, salts, calcium carbonate, calcium sulfate. powdered metals or other reactants for scavenging gas phase contaminants depending on the known contaminants desired to be removed); ion exchange materials, catalytic fillers, and mixtures of the foregoing. For some applications it may be desirable to employ multiple layers of sorbent materials, with each layer containing a different sorbent to selectively remove different contaminants as they pass through the filter.

An adsorbent may also be provided with an indicator that changes color when the adsorbent has been spent. A visual inspection through a transparent film layer 14 may reveal the depth of penetration of the contaminant through the adsorbent, allowing a determination of the level of saturation of the adsorbent. Common indicators include cobalt chloride for moisture detection, O-Tolidine for chloride detection, N, N¹-diphenylbenzidine for detection of nitrous oxides and disodium tetrachloromercurate and methyl red for detection of sulfurous oxides, although any detecting chemical can be utilized.

The first film layer 14 may be any plastic film such as, but not limited to, polyester, polypropylene, PTFE, polyethylene, nylon, polycarbonate, and fluorinated ethylenepropylene (FEP). The first film layer 14 functions to complete the encapsulation of the adsorbent core 12 with the filter layer 10 and to add stiffness to the filter assembly 15. Complementary functions of the first film layer 14 are to complete the waterproof ness of the filter assembly 15 as well as to allow visibility to any indicators that may have been added to detect saturation of the adsorbent.

Figure 2 illustrates an alternate embodiment of the present invention wherein a second film layer 13 is applied to the first plastic film layer 14 The second film layer 13 may be a lower melt thermoplastic or thermoset than the first plastic film layer 14 such as, but not limited to, polyester, PFA, polypropylene, FEP, polyethylene, or any suitable polymer fabric material. Figure 3 illustrates an alternate embodiment of the present invention where a die cut or laser cut hole 20 has been incorporated into the filter assembly 15 for ease of attachment of the filter assembly in an enclosure by means of a post or screw. The first film layer 14 (not shown) helps prevent tearing, fraying, shredding and other destructive actions that would otherwise cause particulation within the enclosure, or loss of precise positioning of the filter assembly The seal area 22 surrounds the hole 20 to keep the adsorbent particulates contained

F. jure 4 illustrates an alternate embodiment of the present invention where die cut or laser cut slots or cross marks 21 are incorporated into the filter for ease of attachment within an enclosure These can be at one end or both ends of the filter assembly Multiple attachments add rigidity in application but take up space that otherwise could be utilized with adsorbent In this embodiment, the property of reduced particulation due to resistance of the first film layer 14 (not shown) to tearing or fraying is even of more importance if the filter is attached with screws through the die cut marks Here again the seal area 22 must surround the cut marks to keep the adsorbent particulates contained

Figure 5 shows yet another embodiment of the present invention wherein a filter support layer 11 is added to the filter layer 10 Filter support layer 11 may also aid in the sealing of filter layer 10 to either first film layer 14 or second film layer 13 For example, the filter layer 10 may be laminated to a filter support layer 11 , comprising a non-woven polyester fabric, and then sealed to the first film layer 14

In each embodiment of the present invention, the filter assembly 15 can be configured into any desired shape to fit a corner or available space Figure 6 shows a particular mount and placement of the filter assembly in a preferred location within a computer disk dnve In Figure 6, a computer disk drive 36 is shown with a spinning disk 35 and an actuator arm 34 The sorbent filter assembly 15 is attached to a post 30 with a screw 31 Current computer disk drives spin a disk at a rate of about 5400 to 7200 rpm, and future drives are expected to spin faster as higher rotational speeds increase data seek times and data transfer rates The stiffness and rigidity of the current invention is such that it can be used to channel airflow towards a particulate recirculation filter 33 held in place by "C" channels 32 By directing air into the recirculation filter more air is forced through the filter and faster particle clean up times can be achieved By channeling the air with the adsorbent filter assembly, the adsorbent is positioned alongside a highly mixed turbulent air stream thereby maximizing adsorbent rates of the filter, while maximizing particulate clean up as well Figure 7 is similar to Figure 6, except that the sorbent filter assembly 15 is held in place by "C" channels 37 instead of being screwed into a post "C" channels secure both ends to add rigidity to the air channel d,. ectιng air into the recirculation filter 33, and prevent adsorbent space loss due to holes or mounting crosshairs

Figure 8 shows an alternate mounting location that facilitates use with an indicator chemical that changes color to indicate saturation of the adsorbent Again, the contaminants enter the adsorbent core 12 through the first filter layer 10 (not shown) To ensure that the contaminants travel through the adsorbent core 12 instead of around the core, the adsorbent core 12 may be laminated to the film layer 14 (not shown), or to the second film layer 13 (not shown) which is laminated to the film layer 14 (not shown) A perceptible color change of the indicator relates depth of penetration of a contaminant through the adsorbent core 12 to the level of saturation of the adsorbent core This color change is visible outside the drive through housing hole 41 and a transparent tape seal 42, such as a polyester tape, for example

Figure 9 shows yet another placement of the filter wherein an alternate film 16, similar to layer 13, is laminated to the first film layer 14 but on the side opposite the adsorbent layer to facilitate a means of fastening the filter to the enclosure housing Here the layer 16 can be further laminated or sealed to the housing by means of heat, ultrasonics or other means to melt seal the layer 16 onto the housing via a predetermined weld area Furthermore, if the filter is sealed over a hole 41 in the enclosure housing as illustrated in Figure 9, the indicator chemicals will be visible Without intending to limit the scope of the present invention, the apparatus and method of production of the present invention may be better understood by referring to the following examples

EXAMPLE 1 A 70 wt % activated carbon and 30 wt % PTFE adsorbent core was made by the following method 6874 g of Calgon type PCB-G carbon and 69,800 g of deionized H₂0 were mixed in a 115 liter baffled stainless container While the slurry was agitating, 2610 g of PTFE in the form of a 24 8% aqueous dispersion was rapidly poured into the vessel The PTFE dispersion used was AD-059 obtained from ICI Americas, Inc The mixture coagulated within 1 minute and after 2 1/2 minutes the mixer was stopped The coagulum settled to the bottom and the effluent was clear

The coagujm was dried at 160°C in a convection oven ^""^"he dried cake was chilled below 0°C It was hand ground through a 635 cm stainless mesh screen Next, 0 701 g of mineral spirits was added per gram of filled powder The mixture was chilled, passed through a screen again, tumbled then allowed to sit for greater than 16 hours at ambient conditions

A 10 6 cm diameter pellet was formed in a cylinder at 860 psi The pellet was heated approximately 16 hours at 49°C The pellet was then extruded into tape The tape was then calendared between heated rolls to a thickness of 0 127 cm The bulk of the lubricant was evaporated by running the tape across heated rollers The partially dried tape was then solvent extracted in isopropanol in a sonicated bath The isopropanol was removed in a vacuum oven The tape was then slit to 0 794 cm width by running a 10 cm width through a blade box The final tape density was 0 75 g/cc

A filter layer tape was made in accordance with the above procedure except 1453 g of PFA solids in the form of a 22 7% aqueous dispersion was added to 50,000 g of H₂0 7247 g of PTFE solids in the form of 23 7% aqueous dispersion was rapidly poured into the vessel The PTFE dispersion used was type AD-059 obtained from ICI Americas, Inc After 1 minute of mixing, 14 6 g of polyethylene imine was added to induce co-coagulation Total mixing time was one minute and forty seconds

The cake was dried at 165^βC, chilled, screened, and lubricated at 0 175 g of mineral spints per gram of filled powder The mixture was chilled, screened, left at ambient for 16 hours and then pelletized The pellet was heated to 49^βC for 16 hours and extruded into tape form The tape was calendared through rolls to 0 046 cm The lubricant was removed by evaporating across heated rolls in 2 passes On the second pass, the tape was expanded at a 2 1 ratio at 105 feet per minute (32 0 m/min) and a maximum temperature of 275°C The tape was then stretched across two heated surfaces at 340°C at 25 1 and 2 1 expansion ratios and an output speed of 75 ft/mm (22 86 m/min) The expanded tape was 0 0025 cm thick and approximately 0 7 g/cc A 1 2 mil (0 03 mm) thick heat seal adhesive on 5 mil (0 127 mm) thick polyester film was purchased from Lamart Corporation Clifton, New Jersey Sampler were made frorr these three layers similar to Figure 3 where total filler length was 1 1875" (30 1625 mm), total width was 0 5" (12 7 mm), adsorbent core length was 0 75" (19 05 mm) and adsorbent core width was 0 3125" (7 9375 mm) The die cut hole was 0 090" (2 286 mm) in diameter and the welded area around the hole was similar to that displayed in Figure 3

Although a few exemplary embodiments of the present invention have been described in detail above, those skilled in the art readily appreciate that many modifications are possible without materially departing from the novel teachings and advantages which are described herein Accordingly, all such modifications are intended to be included within the scope of the present invention, as defined by the following claims

Claims

What is claimed is

1 A sorbent filter assembly for selectively sorbing contaminants present in an environment, the sorbent filter assembly comprising a filter layer comprised of a porous material which is adapted to permit vapor contaminants to diffuse therethrough, a sorbent core, and a first plastic film layer, wherein the sorbent core is disposed between the filter layer and the first film layer, and wherein the filter layer and the first film layer are adapted to fasten to each other to fully encapsulate the sorbent core

2 The invention of Claim 1 further comprising a filter support layer disposed between the filter layer and the first film layer 3 The invention of Claim 1 , wherein the filter layer is comprised of at least in part polymeric filter media selected from a group consisting of polypropylene membrane, nylon membrane, polycarbonate and polyester membrane, mixed cellulose ester membrane, cellulose triacetate membrane, and polyethylene 4 The invention of Claim 1 , wherein the filter layer is a porous polytetrafluoroethylene (PTFE) membrane

5 The invention of Claim 4, wherein the porous PTFE membrane is filled with a thermoplastic material

6 The invention of Claim 4, wherein the porous PTFE membrane is filled with a thermoset material

7 The invention of Claim 4, wherein the porous PTFE membrane is a filled with perfluroalkyl copolymer (PFA)

8 The invention of Claim 1 , wherein the sorbent core comprises elements selected from a group consisting of loosely packed particles, adsorbent particles in a binder, a scaffold of porous polymeric material having void spaces filled with sorbent, sorbent impregnated woven or nonwoven fabrics, porous castings of sorbents and fillers, and carbon fabric

9 The invention of Claim 1 wherein the sorbent core comprises adsorbent filled PTFE membrane 10 The invention of Claim 1 wherein the sorbent core comprises adsorbent filled polyethylene membrane

1 I The invention of Claim 1 , wherein the first film layer is selected from a group consisting of polyester polypropylene PTFE, polyethylene nylon polycarbonate, and fluorinated ethylene propylene (FEP)

12 The invention of Claim 1 , wherein the sorbent core comprises a physisorber

13 The invention of Claim 1 , wherein the sorbent core comprises a chemisorber 14 The invention of Claim 1 , wherein the sorbent core comprises of an ion exchange material

15 The invention of Claim 1 wherein the sorbent core comprises a catalytic material

16 The invention of Claim 1 wherein the sorbent core comprises an adsorbent saturation indicator that indicates saturation of the adsorbent

17 The invention of Claim 16, wherein the indicator is selected from a group consisting of cobalt chloride, 0-tolιdιne, N-N¹-dιphenylbenzιdιne, disodium tetrachloromercurate and methyl red

18 The invention of Claim 2, wherein the filter support layer comprises a polymer fabric

19 The invention of Claim 18, wherein the polymer fabric is polyester

20 The invention of Claim 1 further comprising a second film layer of polymeπc material laminated to the first film layer

21 The invention of Claim 20, wherein the material is selected from a group consisting of polyester, PFA, FEP, polypropylene, and polyethylene

22 The invention of Claim 16, wherein the sorbent filter assembly further comprises an enclosure defining an area of transparency, and wherein the filter assembly is visibly mounted in the enclosure such that the adsorbent saturation indicator can be seen from outside enclosure through the area of transparency

23 The invention of Claim 1 further comprising an alternate layer of polymeric material laminated to the first film layer on the side opposite the adsorbent to faciliate the melt sealing of the filler to the housing enclosure

24 The invention of Claim 23 wherein the sorbent filter assembly is mounted over an aperture in an enclosure wherein the sorbent filter assembly is visibly mounted over the hole such that the adsorbent saturation indicator can be seen from outside the enclosure through the area of transparency

25 The invention of Claim 23, wherein the alternate ,ayer is selected from a group consisting of polyester, PFA, FEP, polypropylene and polyethylene

26 The invention of Claim 1 , wherein the sorbent filter assembly is air directedly mounted to direct air flow in a computer disk drive through a particulate recirculation filter to maximize the adsorption rate of the sorbent core and to enhance the performance of the particulate recirculation filter 27 An improved computer disk drive, wherein the improvement comprises a sorbent filter assembly having a filter layer, a sorbent core, and a first film layer, wherein the sorbent core is disposed between the filter layer, and the first film layer and wherein the filter layer and the first film layer are adapted to fasten to each other to fully encapsulate the sorbent core; and a particulate recirculation filter, wherein the sorbent filter assembly is airflow directedly mounted in the disk drive to direct airflow into the particulate recirculation filter to maximize the performance of both the sorbent filter assembly and the particulate recirculation filter.