WO1999004884A1

WO1999004884A1 - High flow absorbent breather filter

Info

Publication number: WO1999004884A1
Application number: PCT/US1998/015045
Authority: WO
Inventors: Edwin Dauber; Sara Pineo; Glenn Shealy
Original assignee: Gore Enterprise Holdings, Inc.
Priority date: 1997-07-22
Filing date: 1998-07-22
Publication date: 1999-02-04
Also published as: AU8576898A

Abstract

A compact high air flow, or low resistance to air flow, filter is disclosed that serves both the function of inlet, or particulate filtering, breather filter and adsorbent filter. The novel filter is particularly low in outgassing and nonvolatile residues, as well as low in particulation.

Description

TITLE OF THE INVENTION

HIGH FLOW ABSORBENT BREATHER FILTER

FIELD OF THE INVENTION

The present invention is an improved device for filtering particulates and vapor phase contaminants, thus preventing such materials from entering a confined environment such as electronic or optical devices which are susceptible to contamination (e.g. computer disk drives). The improved device of the present invention incorporates the two functions of inlet, or breather, filter and sorbent filter in a unique high air flow, or low resistance to air flow, configuration.

BACKGROUND OF THE INVENTION

Many enclosures that contain sensitive instrumentation must maintain very clean environments in order to allow the instruments to operate properly. Examples include, but are not limited to, enclosures with sensitive optical surfaces, or electronic connections 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, or corrosive vapors; and electronic control boxes such as those used in automobiles and industrial applications that can be sensitive to particles, moisture buildup, and corrosion as well as contamination from fluids and vapors. Contamination in such enclosures can originate from both inside and outside the enclosures. For example, in computer hard drives, damage may result from external contaminants as well as from particles and outgassing generated from internal sources.

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 stopped. Newer high density disks are more sensitive to contamination-caused stiction because they are smoother and only thin layers of lubricants are used. Contaminants on the disk change the surface energy and the adhesive forces between the head and disk, which cause stiction. Also, vapors that condense in the gap between the head and disk can cause stiction. Further exacerbating these effects are the newer lower energy, lower torque motors being used in smaller disk drives for portable computers. Even before stiction occurs, problems with increased friction resulting in increased start-up torque can be problematic.

Another serious contamination-related failure mechanism in computer disk drives is head crashes. Head crashes can occur when particles get into the head disk interface. Newer high density drives typically have 2 micro inches (0.51 mm) or less flying heights or spacing between the head and disk during operation and typically have disk rotating up to 10,000 revolutions per minute with even higher rpm's planned. Even submicron sized particles can be a problem, causing the head to crash into the particle or the disk after flying over a particle, bringing the drive to an abrupt failure mode. Further, even particles that do not cause head crashes can cause thermal asperities and result in unusable storage areas at these locations on the disks.

Internal particulate filters or recirculation filters are also well known. Typically, they are pieces of filter media such as expanded polytetrafluoroethylene (PTFE) membrane laminated to a polyester nonwoven backing material or pillows of electret electrostatic filter media that are pressure fit into slots or "C" channels and are placed in the active air stream, such as near the rotating disks in a computer hard disk drive or in front of a fan in electronic control cabinets, etc. Alternatively, the filter media can be framed in plastic frames. These filters work well for the removal of internally generated particles, but do not address the problem of internally generated vapor phase contaminants.

Internal adsorbent filters are also well known. One example is described in U.S. Patent No. 4,830,643, issued to Sassa et al. This patent is directed to a sorbent filter wherein a powdered sorbent or sorbent mixture is encapsulated in an outer expanded PTFE tube. This filter is manufactured by W. L. Gore & Associates, Inc., Elkton, Maryland, and is commercially available under the trademark GORE-SORBER® module. While this filter is highly effective at collecting vapor phase contaminants, it is currently only available in filter volumes down to about 3 cc. This filter works well for internally generated vapors, but does not prevent vapors from the environment from entering the enclosure.

A second well known internal adsorbent assembly incorporates a layer of adsorbent such as activated carbon/PTFE composite between an encapsulating filter layer and layer of pressure sensitive adhesive that helps encapsulate the adsorbent, as well as providing a means of mounting the adsorbent assembly on an interior wall in the enclosure. One example is described in U.S. Patent No. 5,593,482, issued to Dauber et al. This filter is manufactured by W. L. Gore & Associates, Inc., Elkton, Maryland, and is commercially available under the trademark GORE-TEX® adsorbent assembly.

A third internal adsorbent assembly incorporates a layer of adsorbent such as activated carbon/PTFE composite between two layers of filter media or is alternatively wrapped in a layers of filter media and can be installed between slots or "C" channels much the way a recirculation filter is installed, but without significant air flow through the filter. One example is described in U.S. Patent No. 5,500,038, issued to Dauber et al., and is again commercially available from W. L. Gore & Associates, Inc, Elkton, Maryland.

A newly introduced internal adsorbent recirculation filter which incorporates activated carbon beads glued to a nonwoven carrier that is sandwiched between two layers of electret filter material and two layers of plastic support screen is also available. This filter provides some sorbent protection at the sacrifice of some filtration effectiveness, as it adds some resistance to air flow to the recirculation filter.

Additionally, a washable internal adsorbent recirculation filter is described in U.S. Patent No. 5,538,545, to Dauber et al. It is commercially available from W. L. Gore & Associates, Inc. under the trademark GORE-TEX® adsorbent recirculation filter.

All of the filters described above address internal contaminants in a device, such as in sensitive instrumentation. However, in addition, disk drives must be protected against a large amount of contaminants in the surrounding environment that can penetrate the drive. This is true for drives used in small to medium sized computer systems which may not be used in the typical data processing environment, and is especially true in drives that are removable and portable to any environment, such as disk drives that are used in laptop computers or in Personal Computer Memory Card International Association (PCMCIA) slots.

Filtration devices to keep particles from entering these enclosures are well known. They may consist of a filtration media held in place by a housing of polycarbonate, acrylonitrile butadiene styrene (ABS), or some other material, or they may consist of a filtration media in the form of a self-adhesive disk utilizing a layer or layers of pressure sensitive adhesive. These devices are mounted and sealed over a vent hole in the enclosure to filter particulates from the air entering the drive. Filtration performance depends not only on the filter having a high filtration efficiency but also on having a low resistance to air flow so that unfiltered air does not leak into the enclosure through gaskets or seams in the device, instead of entering through the filter. While such filters work well for particulates, they do not address the problems mentioned earlier with respect to vapor phase contaminants. Combination sorbent breather filters to keep particulates and vapors from entering enclosures are also known. These combination filters are made by filling a cartridge of polycarbonate, ABS, or similar material with sorbent and securing filter media on both ends of the cartridge. Examples of such filters are described in U.S. Patent No. 4,863,499, issued to Osendorf (an anti-diffusion chemical breather assembly for disk drives with filter media having a layer impregnated with activated charcoal granules); U.S. Patent No. 5,030,260, issued to Beck et al. (a disk drive breather filter including an assembly with an extended diffusion path); and U.S. Patent No. 5,124,856, issued to Brown et al. (a unitary filter medium with impregnated activated carbon filters to protect against organic and corrosive pollutants). Unfortunately, many of these designs are relatively thick (i.e., about 0.5 inches or greater), and thus would take up too much space in today's miniaturized drives.

A second combination adsorbent breather filter is also well known wherein the adsorbent material, such as an impregnated activated carbon/ PTFE composite layer, is encapsulated between two layers of filter media and is applied over a hole in the enclosure of a device with a layer of pressure sensitive adhesive. These filters work well when drives are well sealed, and they are of a size that can be used in today's small drives. Moreover, because these filters are typically designed to filter air coming into the drive, the adsorbent is typically desired to adsorb both organic and corrosive vapors from the outside environment and will filter particulates from air entering or leaving the drive. However, limitations in air flow still exist with these filters.

A third combination adsorbent breather filter similar to the second combination described above utilizes Kynol® or treated Kynol® activated carbon as the adsorbent layer. Kynol is a registered trademark of Kynol America, Inc. This carbon is characteristically very dusty; however, it is typically laminated with a filter material such as expanded PTFE membrane on both sides prior to converting into adsorbent breather filters. A significant problem with these current adsorbent breather filters is they are either too thick, as with those using plastic boxes, or are too restrictive or resistant to air flow. Resistance to air flow is very important in devices with higher propensity to leak around seals or gaskets in the device. For example, unfiltered air can enter a disk drive through leak paths around seals and gaskets if the resistance of the inlet adsorbent breather filter is too high.

What is needed is an improved high flow, or low resistance to air flow, adsorbent breather filter for use in today's inexpensive yet highly sophisticated devices, such as computer hard disk drives.

SUMMARY OF THE INVENTION

The present invention is a compact high air flow, or low resistance to air flow, filter that serves both the function of inlet, or particulate filtering, breather filter and adsorbent filter. Furthermore, the novel filter of the present invention can be made to be particularly clean or low in outgassing and nonvolatile residues, as well as low in particulation. In some embodiments, the filters of the present invention have the added benefit that they can be washed with deionized water to remove surface ionic contamination and particulation to improve their suitability for those applications requiring high cleanliness, such as in computer disk drives. In a preferred embodiment of the present invention, the filter comprises a layer or layers of adhesive, such as pressure sensitive, hot melt, thermoplastic, or other suitable adhesive, to adhere the filter to the proper location on the enclosure or housing of a device requiring an adsorbent breather filter. For example, the filter may be adhered to an interior wall of the enclosure, and may also possibly cover an inlet diffusion tube groove which may be present in the device. The filter of the present invention further comprises a layer or layers of filter media with low resistance to air flow and reasonably high efficiency. In a preferred embodiment, the filter media has a filtering efficiency capable of filtering particles of 0.3 micron at 99.97% efficiency. The filter further comprises a sorbent material. In one embodiment, the sorbent may be located between the adhesive and filter layers. For example, in one configuration, the adhesive may be provided around a circumference of a surface of the sorbent layer of the filter to provide an adhesive attachment means for the filter, while allowing the flow of air into the enclosure through the non-adhered portion. In a preferred embodiment, the face velocity air flow of the finished filter is equal to or greater than 0.8 ft/min at a resistance of 0.5" H₂0.

BRIEF DESCRIPTION OF THE DRAWINGS

The operation of the present invention should become apparent from the following description when considered in conjunction with the following drawings, in which:

Figure 1 is a top view of an embodiment of a filter of the present invention, as it would appear when affixed to an enclosure housing;

Figure 2 is a side cross-sectional view of an embodiment of a filter unit of the present invention, as it would appear when affixed to an enclosure housing;

Figure 3 is a side cross-sectional view of an embodiment of a filter of the present invention as it would appear when installed in a computer hard disk drive;

Figure 4 is a schematic of a test rig and procedure for determining the leakage of particles into a drive around the adsorbent breather filter of the present invention; and Figure 5 is a table of data generated from the test rig illustrated in

Figure 4. DETAILED DESCRIPTION OF THE INVENTION

The present invention is an improved high air flow, or low resistance to air flow, combination adsorbent breather filter capable of removing particulates and vapor phase contaminants from air entering an enclosure from the surrounding environment to protect sensitive equipment present within the interior of the enclosure. The filter of the present invention can be made to be particularly clean, in that it is very low in outgassing or nonvolatile residues, low in particulation, and may be washed in certain embodiments with deionized water, if necessary, to remove ionic contamination from the surface of the filter without removing adsorbent components which may be present to aid, for example, in the chemisorbtion of corrosive acid gases.

As mentioned earlier herein, the resistance to air flow of an adsorbent breather filter is an important aspect or property of the filter. This can be demonstrated by the experimental rig and procedure shown in Figure 4. Figure 4 shows a hard disk drive 40 where air is withdrawn from the drive 40 through an access port 41 by a laser aerosol spectrometer 42, such as a PMS-LASX spectrometer made by Particle Measurement Systems, Inc, in Boulder CO.. The laser aerosol spectrometer 42 counts the number of particles 44, as well as sizes them in numerous size channels from 0.12 μm to approximately 3 μm in diameter. Air enters the drive 40 through the adsorbent breather 43 in the direction indicated by arrow 46, as well as through any other weak seal areas 48 with resistance to air flow low enough to allow air into the drive 40. Air entering the drive through the adsorbent breather filter 43 will be filtered of vapors and particulates 44. Air entering through other leakage points is unfiltered. Thus, the higher the particle counts recorded by the laser aerosol spectrometer 42, the greater the indication that more air enters through unfiltered leakage points than through the intended adsorbent breather filter 43.

Results of tests for both drives sealed with an elastomeric gasket and with an adhesive tape seal are shown for breather filters and adsorbent breather filters of various permeabilities, or resistance to air flow, in Figure 5. As can be seen from the data, the optimum cleanliness is approached when the face velocity at 0.5 inch H₂0 for the breather filter or adsorbent breather filter over a 0.125" diameter hole in the drive is at or above 0.8 feet/minute, conventional adsorbent breather filters have been typically specified @ 0.15 to 0.3 feet/minute at 0.5 inch H₂0 pressure, because that was the highest air flow material that had been commercially available until the novel materials of the present invention. A significant value of the present invention is that designs with less expensive seals will be possible due to the use of the high flow, or low resistance, carbon breather of the present invention. Moreover, the ability to make very thin, or low profile filters in the present invention permits filter design flexibility which was heretofore unachievable with the materials of the prior art. For example, the filters of the present invention may be made with overall thicknesses of about 0.1 inch or less, more preferably about 0.06 inch or less, and even as low as about 0.03 inch or less. Correspondingly, the sorbent materials of the present invention may be made with thicknesses as low as about 0.95 inch or less, preferably as low as about 0.05 inch or less, even more preferably as low as about 0.01 inch or less, and even as low as about 0.005 or less. Various examples of the present invention can be described and illustrated in the accompanying drawings and discussions.

Figure 1 shows an example of a top view of a first embodiment of the high flow adsorbent breather filter 10 of the present invention as it would be mounted with an adhesive region 14 over a hole 11 in an enclosure 12 for housing sensitive equipment, or the like. Air flow into the drive would be through the hole 11 and filter 10 into the enclosure 12.

Alternatively, instead of an enclosure having a simple inlet hole 11 , such as shown in Figure 1 , the enclosure could include a diffusion tube upstream of the filter to help extend the organic or acid gas life of the sorbent in the filter by protecting it during times of no flow, i.e. by creating a diffusion barrier so that the sorbent remains relatively unchallenged by the outside contaminants during times of little or no air flow, sometimes referred to as "rest."

More detail of the features and functioning of the invention can be seen in Figure 2, which shows a side view of another embodiment of a filter assembly 20 of the present invention as it would appear mounted on a portion of an enclosure housing 34. Air passes into the drive by air flow path 31 coming from outside the enclosure through a diffusion tube 30 and then through the adsorbent breather filter 20. The adhesive layer 25 mounts the filter 20 to the housing and has a hole 24 in the adhesive to allow the air to flow through the filter. Layer 27 is a filter media, layer 26 is an adsorbent layer, and layers 28 and 29 are filter layers that are employed in this embodiment to encapsulate the adsorbent and prevent particulation of adsorbent through either side of the filter. While these layers are representative of one possible configuration of the filter of the present invention, it would be apparent to an artisan of skill in the art that the layers may be incorporated in any suitable configuration which provides the beneficial high air flow, filtering and sorbtion features of the present invention.

Figure 3 is a side cross-sectional view of the adsorbent breather filter shown in Figure 2 incorporated into a computer hard disk including rotating magnetic recording disks 21, read/write heads 22 and the armatures 23 for moving the heads.

As mentioned earlier herein, an adhesive, such as pressure sensitive, hot melt, thermoplastic, or other suitable adhesive, is used to adhere the filter to the proper location on the enclosure or housing of a device. The adhesive layer may be either a single layer of transferable adhesive or a double-sided adhesive coated onto a carrier or substrate, such as polyester or polypropylene. A preferred adhesive utilizes a high peel strength of greater than 30 ounces/inch as measured by PSTC # 1 (Pressure Sensitive Tape Council), low outgassing of less than 0.1 % collected volatile condensable material (CVCM) as measured by ASTM-E595-84, solvent free nonparticulating permanent acrylic pressure sensitive adhesive. A double-sided adhesive tape may be preferred in xome instances because it is easier to handle, and the substrate adds support and rigidity to the filter construction. One commercially available adhesive satisfying these requirement is 3M 444 adhesive, available from Minnesota Mining & Manufacturing in Minneapolis, MN. Other adhesives, such as UV curable adhesives, etc. are also suitable, as are hot melt or thermoplastic type adhesives.

The adsorbent may comprise one or more layers of 100 % adsorbent material, such as granular activated carbon, or may be a filled product matrix such as a scaffold of porous polymeric material compounded with adsorbents that fill the void spaces. Other possibilities for the adsorbent material include adsorbent impregnated nonwovens, such as cellulose or polymeric nonwovens that may include latex or other binders, as well as porous castings of adsorbents and fillers that are polymeric or ceramic. Another possible sorbent is a woven or nonwoven material that is carbonized, such as that available from Kynol America, New York, New York. The adsorbent can also be a mixture of different types of adsorbents. A particularly preferred embodiment of the sorbent of the present invention utilizes a sorbent filled PTFE sheet wherein the sorbent particles are entrapped within an expanded PTFE structure, such as is taught in U.S. Patent No. 4,985,296, issued to Mortimer, Jr., and which is incorporated by reference herein. Preferably, particles are packed in a multi- modal (e.g. bi-modal or tri-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, so as to maximize the amount of active material contained in the sheet or matrix. This technique also allows a number of different sorbents to be filled into a single layer. The PTFE sheet is then expanded to allow high air flow through the layer. Expanding the sorbent matrix reduces loading density, but offers a more uniform sorbent layer. Using PTFE as a binder material for the sorbent matrix imparts a number of additional advantages to this improved filter construction. First, PTFE is hydrophobic. Some adsorbents used in industry use a water soluble salt to impregnate a physical adsorbent, such as activated carbon to provide a chemical adsorbent with a large active surface area. By impregnating the carbon in the PTFE/adsorbent matrix, it makes the final matrix water resistant, so that deionized water can be contacted with the sorbent layer, but not penetrate the matrix. Thus, the salt treatment is not susceptible to removal by water washing. Ionic contamination has become a big concern for corrosion- susceptible apparatus, such as computer disk drives. Particular ions of concern, such as chlorine and sulfur dioxide, are readily soluble in water, and thus a deionized water wash has become routine for many components used within the drive. Thus, embodiments utilizing a sorbent retained in an expanded PTFE matrix and/or PTFE filter layers are constructions that can use water soluble, salt treated adsorbents incorporated into the adsorbent layer that can withstand subsequent washing without loss of adsorbent treatment and effectiveness.

Additionally, PTFE is a noniinting, nonoutgassing inert binder that effectively reduces dusting of sorbent material during the manufacture and during the life of the filter. This material can also be made in a relatively thin, highly loaded material in accordance with U.S. Patent No. 4,985,296, thus allowing the formation of thin final constructions with high sorbent content. The PTFE/sorbent composite can easily be made in thickness' from less than 0.001 inch to 0.250 inch, and greater, allowing a great deal of flexibility in finished filter thickness and sorbent loading. Additionally, sorbent densities approximating 80-90% of full density are possible with multi-modal packing and physical compression, so that maximum sorbent material can be packed per unit volume. The use of PTFE as the binding element also does not block the sorbent pores, as typically occurs with binders such as acrylics, melted plastic resins, and the like.

Examples of sorbent material that may be contained within the sorbent layer include: physisorbers (e.g. silica gel, activated carbon, activated alumina, molecular sieves, etc. ); chemisorbers (e.g. potassium permanganate, calcium carbonate, calcium sulfate, sodium carbonate, potassium carbonate, sodium hydroxide, calcium hydroxide, powdered metals or other reactants for scavenging gas phase contaminants); ion exchange materials; catalytic fillers; as well as mixtures of these materials. For some applications, it may be desirable to employ multiple layers of sorbent materials, with each layer containing different sorbents to selectively remove different contaminants as they pass through the filter.

One preferred filter media to encapsulate the adsorbent layer, such as the layers 27 and 28 depicted in Figure 2, is an expanded PTFE membrane made in accordance with U.S. Patent No. 3,953,566, issued to Gore, which is specifically incorporated herein by reference. Alternatively, other filter media, such as polypropylenes, electret filter media, or other high efficiency filter media may be used. Moreover, as mentioned earlier herein, hydrophobic media, such as PTFE membranes, allow deionized water washing without removal of the chemisorbtive treatments often included in the absorbtive layer. A preferred construction for the adsorbent layer and encapsulating layers, such as that depicted as layers 26, 27 and 28 of Figure 2, is through the use of a single co-extruded unit, as will be described in Example 1.

Without intending to limit the scope of the present invention, the present invention may be better understood by referring to the following example: Test Method - AIR FLOW

Air flow was measured by clamping a test sample in a gasketed flanged fixture which provided a circular area of approximately 1/2 inch diameter for air flow measurement. The upstream side of the sample fixture was connected to a flow meter in line with a source of dry compressed air. The downstream side of the sample fixture was open to the atmosphere.

Testing was accomplished by applying a pressure of 0.25 pounds per square inch to the upstream side of the sample and recording the flow rate of the air passing through the in-line flowmeter (a ball-float rotameter). This recorded flow rate was then adjusted for a pressure of 0.5 inches of water by converting from pounds per square inch to inches of water, assuming a linear relationship between flow rate and pressure in this flow rate range.

The sample was conditioned at 70°F and 65% relative humidity for at least 4 hours prior to testing.

Example 1

An approximate 64 weight % treated activated carbon and 36 weight % PTFE adsorbent material was made by the following method: 15.75 pounds (7,150.5 g) of Westvaco activated carbon and 6.6 pounds (2,996.4 g) of sodium carbonate in 60 liters of deionized water was mixed in a 115 liter baffled stainless container for 20 minutes. While the slurry was agitating, 9 pounds (4,086 g) of PTFE in the form of 24.8% aqueous dispersion was rapidly poured into the vessel. The PTFE dispersion was TE-3737 obtained from E. I. duPont de Nemours and Company, Inc. This was mixed for another 90 seconds. The resulting co-coagulum was placed in a tray and the free water was drained off.

The co-coagulum was dried at 80° C and 50 Torr under a nitrogen purge until the powder had less than 0.5 weight % water (about 3 days). The dried cake was chilled to -17° C, then was hard ground and screened through a % inch (6.35mm) screen. About 1.22 pounds (553.9 g) of mineral spirits was added per pound (454 g) of screened co-coagulum. This mixture was again chilled at -17 ° C for about 1 day. The material was then tumbled for 10 minutes, screened through a % inch (6.35mm) screen and allowed to sit for about 1 day. This activated carbon/PTFE co-coagulum was then co-pelletized with a

TE-3737PTFE coagulum that was similarly made and independently lubricated with 0.24 pounds (109g) of mineral spirits per pound (454g) of PTFE in the following way: A dual cylinder pellitizer was used to achieve a pellet with an outer diameter of 4 inches and an inner core having a 3 inch diameter. The lubed

PTFE coagulum was added to the outer annulus between the pellitizer and the inner tube. Then the carbon/PTFE cocoagulum was added into the inner cylinder, and the inner cylinder was removed. This pellet was then loaded into a ram extruder and extruded at 10 gpm through an 80 mil (2.03 mm) duckbill die at about 2200 psi pressure. The tape was then calendered between heated rolls to a thickness of about 0.028 inch (0.71 mm).

This material was then simultaneously dried and expanded linearly at an about 4:1 ratio at high temperature (drying zone of 180 ° C and expansion zone at 250 ° C). Each zone was 10 feet (3.05m), long and the tape speed was 50 fpm (15.2 m/min). The material was then sintered with a two zone sintering at 250° C and 370° C, respectively, in 10 foot (3.05 m) zones, again at a speed of 50 fpm (15.2 m/min).

This material was used for layers 26, 28, and 29, as depicted in Figure 2. This layer had a resulting air flow of 1.4 fpm at 0.5 inch H₂0. This material was combined with a cover filtration layer 27, as shown in Figure 3, made in accordance with U. S. Patent No. 3,953,566, mentioned earlier herein, and a 3M 444 adhesive, also mentioned earlier, with the use of steel roll dies and a clicker press to cut the material layers, then the layers were assembled as shown in Figure 2. The cover filtration layer had an airflow of 18 feet/minute at 0.5 inch H₂O. The finished adsorbent breather filter had an air flow of 1.0 feet/minute at 0.5 inch H₂0 and a particle filtration efficiency of 99.97% at 0.3 micron sized particles, as measured by a PMS - LASX laser aerosol spectrometer made by Particle Measuring Systems, Inc. in Boulder, CO. The filters made had an adhesive ring with an inner diameter of 0.5 inch

(12.7 mm) and an outer diameter of 1.0 inch (25.4 mm). The adsorbent layer had a diameter of 0.7 inch (17.8 mm) that covered the 0.5 inch hole in the adhesive. The cover filtration layer covers the 1.0 inch (25.4 mm) outer diameter, thus encapsulating the carbon particle-containing layer between the cover filtration layer, adhesive layer and the pure PTFE layer of the coextrusion facing the adhesive.

These filters contained about 6 mg of treated activated carbon that was capable of adsorbing 1.2 mg of H₂S at 40 ppm concentration at 50% RH, as the adsorbent layer was on the order of 64% treated activated carbon in the coextruded state.

In summary, the present invention provides a higher flow adsorbent breather filter than is now available and can add value to sensitive enclosures by adsorbing vapors and filtering particles from air entering the enclosure and reduce the amount of air bypassing the filter by its high flow or low resistance nature. Although the above description and examples were primarily directed to production of a filter for use in a computer disk drive application, the present invention can be used in many other applications, for example, electronic control boxes, automobile filters to allow makeup air, optical instrumentation, etc., that require air to go in and out of the enclosure for pressure equilibration. While particular embodiments of the present invention have been illustrated and described herein, the present invention should not be limited to such illustrations and descriptions. It should be apparent that changes and modifications may be incorporated and embodied as part of the present invention within the scope of the following claims.

Claims

We claim:

1. An adsorbent breather filter comprising: an adhesive; an adsorbent; and at least one filtration means, wherein said filter has an overall air flow therethrough of than 0.8 ft/min or greater at 0.5 inches of water pressure.

2. The adsorbent breather filter of claim 1 , wherein said filtration means comprises PTFE.

3. The adsorbent breather filter of claim 2, wherein said filtration means comprises expanded PTFE.

4. The adsorbent breather filter of claim 1 , wherein said filter has an overall thickness of about 0.1 inch or less.

5. The adsorbent breather filter of claim 1 , wherein said filter has an overall thickness of about 0.6 inch or less.

6. The adsorbent breather filter of claim 1 , wherein said filter has an overall thickness of about 0.3 inch or less.

7. The adsorbent breather filter of claim 1 , wherein said adsorbent has a thickness of about 0.095 inch or less.

8. The adsorbent breather filter of claim 1 , wherein said adsorbent has a thickness of about 0.05 inch or less.

9. The adsorbent breather filter of claim 1 , wherein said adsorbent has a thickness of about 0.01 inch or less.

10. The adsorbent breather filter of claim 1 , wherein said adsorbent has a thickness of about 0.005 inch or less.

11. The adsorbent breather filter of claim 1 , wherein said adsorbent comprises at least one material selected from the group consisting of a chemisorber, a physisorber, and a combination thereof.

12. The adsorbent breather filter of claim 1 , wherein said adsorbent comprises an expanded PTFE layer and an activated carbon/PTFE composite layer.

13. The adsorbent breather filter of claim 1 , wherein said adsorbent is positioned between said adhesive and said filtration means.

14. The adsorbent breather filter of claim 1 , wherein said filtration means comprises two layers and said adsorbent is sandwiched between said layers of said filtration means.

15. An adsorbent breather filter comprising: an adhesive; an adsorbent; and at least one filtration means capable of filtering particles of 0.3 micron at 99.97% efficiency, wherein said filter has an overall air flow therethrough of 0.8 ft/min or greater at 0.5 inches of water pressure.

16. The adsorbent breather filter of claim 15, wherein said filtration means comprises PTFE.

17. The adsorbent breather filter of claim 16, wherein said filtration means comprises expanded PTFE.

18. The adsorbent breather filter of claim 15, wherein said filter has an overall thickness of about 0.1 inch or less.

19. The adsorbent breather filter of claim 15, wherein said filter has an overall thickness of about 0.6 inch or less.

20. The adsorbent breather filter of claim 15, wherein said filter has an overall thickness of about 0.3 inch or less.

21. The adsorbent breather filter of claim 15, wherein said adsorbent has a thickness of about 0.095 inch or less.

22. The adsorbent breather filter of claim 15, wherein said adsorbent has a thickness of about 0.05 inch or less.

23. The adsorbent breather filter of claim 15, wherein said adsorbent has a thickness of about 0.01 inch or less.

24. The adsorbent breather filter of claim 15, wherein said adsorbent has a thickness of about 0.005 inch or less.

25. The adsorbent breather filter of claim 15, wherein said adsorbent comprises at least one material selected from the group consisting of a chemisorber, a physisorber, and a combination thereof.

26. The adsorbent breather filter of claim 15, wherein said adsorbent comprises an expanded PTFE layer and an activated carbon/PTFE composite layer.

27. The adsorbent breather filter of claim 15, wherein said adsorbent is positioned between said adhesive and said filtration means.

28. The adsorbent breather filter of claim 15, wherein said filtration means comprises two layers and said adsorbent is sandwiched between said layers of said filtration means.