WO2007005084A2

WO2007005084A2 - Improved filter construction for removing contaminants from an enclosure

Info

Publication number: WO2007005084A2
Application number: PCT/US2006/012838
Authority: WO
Inventors: Peter Roeber; Earl Ball; Edwin Dauber
Original assignee: Gore Enterprise Holdings, Inc.
Priority date: 2005-06-30
Filing date: 2006-04-07
Publication date: 2007-01-11
Also published as: EP1911030A2; CA2612633A1; EP1911030A4; JP2009501650A; WO2007005084A3

Abstract

The invention relates to 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 dis drives) by providing a filter for an improved fit within the enclosure. Filtration functions include a recirculation filter and optional adsorbent recirculation filter.

Description

TITLE OF THE INVENTION

Improved Filter Construction for Removing Contaminants from an Enclosure

FIELD OF THE INVENTION

This invention relates to 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 the fit of the filter to improve its functionality.

BACKGROUND OF THE INVENTION

Many enclosures that contain sensitive instrumentation must maintain very clean environments in order for the equipment to operate properly. Examples include enclosures with sensitive optical surfaces or electronic connections that are sensitive to particles and gaseous contaminants which can interfere with mechanical, optical, or electrical operation. Other examples include data recording devices such as computer hard disk drives that are sensitive to particles, organic vapors, and corrosive vapors. Still others include enclosures for processing, transporting or storing thin films and semiconductor wafers. Also included are 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 originates from both inside and outside the enclosures. For example, in computer hard drives, damage may result from external contaminates as well as from particles and outgassing generated from internal sources. The terms "hard drives" or "hard disk drives" or "disk drives" or "drives" will be used herein for convenience and are understood to include any of the enclosures mentioned above.

One serious contamination-related failure mechanism in computer disk drives is static friction or "suction". Stiction results from the increased adhesion of a drive head to a disk while the disk is stationary plus increased viscous drag parallel to the head-disk interface. Newer high-density disks are more sensitive to contamination-caused stiction because they are smoother and only thin layers of lubricants are present. 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 and consumer applications.

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 have 30 nanometer or less flying heights or spacing between the head and disk during operation and typically have disks rotating 4500 revolutions per minute or greater. 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. Particles can also adversely affect data integrity and mechanical reliability of a drive, sometimes referred to as thermal asperity.

In addition, disk drives must be protected against a large number 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. This is especially true in drives that are removable and portable to any environment such as disk drives that are used in laptop computers, Personal Computer Memory Card International Association (PCMCIA) slots. Newer consumer applications such as car navigation systems and cell phone applications will extend the environmental challenges and therefore, the protection needs for hard disk drives.

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 particles from the air entering the drive. Filtration performance depends not only on the filter having high filtration efficiency but also on having a low resistance to airflow so that unfiltered air does not leak into the enclosure through a gasket or seam instead of entering through the filter. Such filters work well for particles of external origin, but do not address the problems from vapor phase contaminants.

Combination sorbent breather filters to keep particles and vapors from entering enclosures are also well known. These can be made by filling a cartridge of polycarbonate, ABS, or similar material with sorbent and securing filter media on one or more ends of the cartridge. Examples of such filters are described in U.S. Patents 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); 5,030,260 issued to Beck et al. (a disk drive breather filter including an assembly with an extended diffusion path); 5,124,856 issued to Brown et al. (a unitary filter medium with impregnated activated carbon filters to protect against organic and corrosive pollutants); and 5,447,695 issued to Brown et al. (Chemical Breather Filter Assembly). Unfortunately, many of these designs are too large and take up too much space in today's miniaturized drives. They again filter only incoming air of particles and mainly incoming air of vaporous contaminates, although some internal air can also be cleaned from internally generated vaporous contaminates since the filters are inside the drive and these contaminates will diffuse into the adsorbent sections of the filters. None of these filters address cleaning the air of internal particles.

A second combination adsorbent breather filter is also well known that encapsulates the adsorbent material such as an activated carbon impregnated polytetrafluoroethylene (PTFE) composite layer between two layers of filter media and is applied over a hole in the enclosure with a layer of pressure sensitive adhesive. These filters work well and are of a size that can be used in today's small drives but are typically designed to filter air coming into the drive. Thus, the adsorbent is typically primarily desired to adsorb both organic and corrosive vapors from the outside environment and will filter particles only from air coming into or leaving the drive. Internally generated vapors can be adsorbed by these filters, but often times these filters are used in conjunction with another internal adsorbent so they can be smaller in size. Again, particles are also generated inside the drive and are not typically captured by these filters.

A diffusion tube can be included with either the initial particulate breather filter or an adsorbent breather filter as described in U.S. Patent 5,417,743 to Dauber and in US patent 5,997,614 by Tuma et al. Diffusion tubes provide additional protection against vaporous contaminants (including moisture) entering the drive through the breather opening by providing a diffusion barrier in the form of the diffusion tube which creates a tortuous or a longer path for contaminants to diffuse through before entering the drive enclosure. Diffusion tubes reduce the number of contaminants reaching the interior of the enclosure (and/or the adsorbent depending on the location of the filter) and increase the humidity time constants or time required for the enclosure to reach humidity equilibrium with the environment. As used herein, for convenience, the term "diffusion tube" may refer to either a conventional tortuous path or it may refer to a non-tortuous cavity into which incoming air passes before entering the filter.

Internal particulate filters, or recirculation filters, are also well known. These filters are typically pieces of filter media, such as expanded PTFE membrane laminated to backing material such as a polyester nonwoven, or "pillow-shaped" filters containing electret (i.e., electrostatic) filter media. They 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 recirculation filter media can be framed in a plastic frame. These filters work well for particulate removal of internally generated particles but do not address the problem of vapor phase contaminants. A major problem with these filters is that in their simplest form they are press fit into slots or "C" channels as mentioned and sometimes this is not an adequate means of installation. For hard disk drives, manufacturers often have several vendors supplying base plates that contain the slots for installation. Each of those vendors may have multiple molds to mold the base plates. And each manufacturer will also have several filter suppliers that each have their own die cutting tooling. Additionally, each mold has to have a draft angle to be moldable and variations in draft angles also exist. Also it is desirable to be able to install a filter upside down so drafting a filter to fit a molded draft angle often isn't an option. Thus one can see by looking at the tolerance stack-up of all these variables (multiple base plate vendors with multiple molds, base plate variability from a single mold, multiple filter vendors, filter size variability from a single vendor, and draft angles in the molded plates), that it can become impossible to create a filter size spec that all vendors can meet that will snugly fit in installation slots for all base plates from all vendors. This becomes a significant problem for hard drive assembly lines, particularly the more automated they become. Filters are installed in the assembly process, and then the drive assembly passes along to further assembly stations. The drive base plate can have some vibration and shock in moving through other stations. The problem is that if the filter doesn't have an adequate fit within the slots it can become dislodged and fall out of the slots. If the filter is too loose it can simply fall out of the slots. If the filter is too tight the filter can spring out of the slots especially with the added vibration of the base plate moving down an assembly line. If there is then no final check before the lid is placed on the base plate, the drive can be assembled with a misplace filter which will cause the drive to fail when it is put into operation.

Internal adsorbent filters are also well known. One example is described in U.S. Patent 4,830,643 issued to Sassa et al. This patent teaches a sorbent filter where a powdered, granular or beaded 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 is highly effective at collecting vapor phase contaminants, it is currently only available in large and medium sizes like filter volumes down to about 3cc. In its present form, this filter is incapable of fully addressing the growing needs for even smaller and more compact sorbent filters, nor is it designed to filter the internal air of particulate contamination. 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 provides a means of mounting the adsorbent assembly on an interior wall in the enclosure. Such a filter is described in U.S. Patent 5,593,482 issued to Dauber et al. Again neither of these filters address particulate contaminates. A third internal adsorbent assembly incorporates a layer of adsorbent such as activated carbon/PTFE composite between two layers of filter media or is alternately wrapped in a layer of filter media and can be installed between slots or "C" channels much the way a recirculation filter is installed but without much real airflow through the filter. Such a filter is described in U.S. Patent 5,500,038 issued to Dauber et al., and, as with the other filters mentioned, this construction does not provide significant particle capturing capability.

As stated above, all of these internal adsorbent filters work well at adsorbing vapor phase contaminants, but they do not filter particulates very well. They can collect particles by some impaction of particles onto the filter (i.e., by having the larger particles impacting or colliding with the adsorbent filter as particle-laden air speeds around the filters) or by diffusion of particles onto the filter. However, these filters do not perform nearly as well as standard recirculation filters that work by a combination of sieving (mechanically capturing particles too large to pass through the pore structure of the filter), impaction (capturing particle too large to follow the bending air streams around filters or the fibers of the filter), interception (capturing particles that tend to follow the air streams, but are large enough to still intercept a filter fiber or in other words those particles with a diameter equal to or less than the distance between the fiber and the air stream line), and diffusion (capturing smaller particles buffeted about by air molecules in a random pattern and coming into contact with a filter fiber to become collected). These means of air filtration are much more rigorously described in a book entitled "Air Filtration" by R. C. Brown, published by Pergamon Press initially in 1993.

A commercially available adsorbent recirculation filter, available from The Donaldson Company, 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. This filter provides some sorbent protection at the sacrifice of some internal particle filtration effectiveness, as this construction appears to increase resistance to airflow to the filter relative to a conventional recirculation filter. The sorbent capability is limited, however, due to, for example, the constraints of the filter size and the blockage of sorbent surface area by the glue holding the carbon to the carrier. These filters are again placed in between slots or "C" channels and again a major problem with these filters is obtaining the required fit for use in between these slots.

Another issue in today's drives is contamination due to corrosive ions such as chlorine and sulfur dioxide. To adsorb these compounds the adsorbent is typically treated with a salt to chemisorb the contaminants. When the filters described in the preceding paragraph were washed in deionized water, large amounts of these salts were released, making it unacceptable to today's sensitive disk drive environments. An alternative washable adsorbent recirculation filter is described in U.S. Patent 5,538,545 issued to Dauber et al., wherein expanded PTFE membranes or other hydrophobic materials are used to encapsulate the adsorbent. However, even these filters must fit in between slots of "C" channels and as already previously stated this is a major problem.

Combinations of several filters having different functions in a single drive have been taught. For example, U. S. Patent No. 5,406,431 , to Beecroft, describes a filter system for a disk drive that includes an adsorbent breather and recirculation filter in specifically identified locations within the drive. Also, U. S. Patent No. 4,633,349, by Beck et al., teaches a disk drive filter assembly comprising a dual media drum type filter element in a recirculating filter assembly that surrounds a breather filter. Further, U. S. Patent No 4,857,087, to Bolton et al., teaches incorporating a breather filter in a recirculation filter housing, but has significantly more parts and incorporates a third filter element complete with housings, apertures, and gaskets to accomplish this inclusion. The combinations described in these patents either locate the filter components in separate regions of the disk drive or incorporate space-consuming fixtures to orient the component parts within the drives.

A multifunction filter providing a breather filter and a recirculation filter with optional; adsorbents can solve many of the problems associated with the previous filters. This is described in US Patent No 6,395,073 to Dauber. This is an adequate solution when the space can be found for placing such a combination filter. But sometimes with such limited space particularly in today's smaller drives, the need exists to have individual components that can be individually maximized for its performance. As the drives continue to increase in recording data density and capacity, they continue to become more sensitive to particulate and vaporous contamination, such that the filtration components performance must be individually maximized to meet the more demanding filtration requirements. US Patent Application Publication Number 2004/0006954 describes a filter having a filtering portion through which flowing air passes and particles are filtered from the flowing air, and an insertion portion included at both ends of the filtering portion. The inserted portion is inserted into support grooves in a channel in a disk drive to form a seal. The patent application teaches that since there is no gap between the support groove of the channel and the insertion portion of the filter, all the air flowing toward the filter passes through the filtering portion.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a filter assembly for mounting in a channel within a disk drive enclosure, the filter assembly comprising a filter having at least a first end comprising a first linear edge and a second end opposite the first end, the second end comprising a second linear edge, said filter having a length equal to the minimum distance between the first linear edge and the second linear edge; and at least one flexible projecting element extending from at least one of the first linear edge and the second linear edge for an orthogonal distance equal to at least about 0.005" inches (0.127 mm).

In another aspect, the invention provides a disk drive enclosure having a filter assembly mounted in a channel, the channel having at least two bearing surfaces spaced apart to form a channel having a width, the filter assembly comprising a filter portion having at least a first end comprising a first linear edge and a second end opposite the first end, the second end comprising a second linear edge, the filter portion having a length equal to the minimum distance between the first linear edge and the second linear edge, and an assembly portion comprising at least one flexible projecting element extending from at least one of the first linear edge and the second linear edge, said at least one flexible projecting element contacting the bearing surface of the channel and being deformed thereby.

In yet another aspect, the invention provides disk drive filter assembly comprising a layered construction comprising at least one electret filter layer comprising fibrous electret material, disposed between a first and second polyester non-woven filter layer, a first support layer adjacent to the first polyester non-woven filter layer and a second support layer adjacent to the second polyester non-woven filter layer, said first and second support layer comprising polyethylene screen material; a sealed edge at the perimeter of said layered construction forming a substantially rectangular filter assembly having at least a first and second substantially parallel sealed edges, the filter assembly having a length equal to the distance between the first and second sealed edges, and at least one flexible projecting element projecting outwardly from at least one of the first sealed edge and the second sealed edge for an orthogonal distance of at leastθ.005" (0.127 mm). In still another aspect, the invention provides a disk drive filter assembly comprising: a layered construction comprising at least one filter layer comprising fibrous material, disposed between a first and second functional layer; a sealed edge at the perimeter of said layered construction, the sealed edge forming a substantially rectangular filter assembly having at least a first and second substantially parallel sealed edges, the filter assembly having a length equal to the distance between the first and second sealed edges, and at least one projecting element projecting outwardly or inwardly from at least one of the first sealed edge and the second sealed edge for a distance of at least 0.005" (0.127 mm) 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 profile view of an embodiment of the filter unit of the present invention with full side projecting elements;

Figure 2 is a profile view of another embodiment of the filter unit of the present invention with smaller side projecting elements;

Figure 3 is a profile view of another embodiment of the filter unit of the present invention with multiple side projecting elements;

Figures 4A, and 4B are profile and end views respectively, of another embodiment of the filter unit of the present invention with slits creating multiple projecting elements along the entire sides of the filter;

Figure 5 is a profile view of another embodiment of the filter unit of the present invention with shaped projecting elements;

Figure 6 is a profile view of another embodiment of the filter unit of the present invention with serrated type projecting elements;

Figure 7 is a profile view of another embodiment of the filter unit of the present invention with a three-dimensional shaped projecting element;

Figures 8 and 8A are profile and end views respectively of another embodiment of the filter unit of the present invention with foldable projecting elements;

Figure 9 is a profile view of another embodiment of the filter unit of the present invention with a single projecting element on a single side;

Figure 10 is a top view of an embodiment of the present invention with smaller projecting elements on opposite ends of the filter unit as it is installed between opposing "C" channels with the projecting elements flexed for a spring loaded effect;

Figures 11A and 11B are top and profile views respectively of another embodiment of a filter unit of the present invention with projecting elements that fit in slits of the channels;

Figure 12 is a profile view of another embodiment of the filter unit of the present invention with an overmolded flexible plastic molded onto the bas filter; DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a new, improved filter that can filter the air of particles and vaporous contaminants. The inventive filter features an improved fit which assures that when the filter is installed between slots or "C" channels it will remain in place. The present invention also provides multiple means of obtaining a secured filter fit between slots or "C" channels in a disk drive.

The inventive filters may be a particle filter or recirculation filter or it can include adsorbents and be a combination particle and vapor filter or adsorbent recirculation filter. In a first embodiment, the filter or adsorbent filter has a projecting element or projecting elements that are more flexible than the filter body and extend from an edge or edges of the filter to give an improved spring- loaded type friction fit. Any number of multiple projecting elements can be utilized. In a second embodiment, the entire side or sides of the filter can be tabbed by forming slits into the side to make multiple flexible projecting elements for the interference or "spring loaded" fit. The projecting elements can take any desired shape. The projecting elements can also be of any desired length. One of skill in the art can determine the appropriate projecting element length, depending on such factors as projecting element material, width and overall filter length. Projecting element lengths as small as 0.005" can be used. Projecting elements longer than 0.25" can also be used. Typically projecting element lengths of from 0.020" to 0.125" would be adequate.

In another embodiment the filter can have a projecting element that folds for some portion of its length and provides added interference fit for the filter in the slots or "C" channels, as depicted in Figure 8. In still another embodiment, the filter can have a shaped three dimensional projecting element that again adds to the interference spring loaded fit into the channels such a filter is depicted in Figure 7.

In another embodiment the filter can have a projecting element or projecting elements that fit into added slits in the "C" channels to help hold the filter into the channels. This extends the filter beyond the channels and secures it from sliding out of the channels while the base plate or enclosure may vibrate during an installation assembly line process as seen in Figure 11.

In another embodiment the filter can have a projecting element or projecting elements added to the filter in a post operation that might include gluing projecting elements on, overmolding projecting elements of a moldable material onto the base filter, or other means of adding a projecting element or projecting elements that can help in the press fit or spring loaded post assembly process.

The filters of the present invention are not only simple to use and install, but also low in out gassing and nonvolatile residues and low in pandiculation. In addition, depending on the construction, the filters can have the added benefit that they can be washed with deionized water to remove surface ionic contamination and particles to improve their suitability for those applications requiring such cleanliness such as in computer disk drives without washing out beneficial treatments such as salts which remove acid gases from the air streams. This washability is accomplished by using hydrophobic filter materials to surround the adsorbent layers. "Hydrophobic" as used in this application means the filter materials have a water (or water with surfactant if one is used) entry pressure sufficient to withstand the conditions of conventional washing steps, such as heating, stirring, ultrasonics, etc.

A layer or layers of filter media are provided in substantially laminar relation to filter the recirculating air of particles and has added features to improve the filters fit in the installation application and process. A layer or layers of adsorbent media may optionally be provided alongside the filter layers, or between filter media layers, to filter the recirculating air stream of vaporous contaminants.

Referring now to Figure 1 , there is shown a profile perspective view of a first embodiment of the improved recirculation filter 10 of the present invention. Figure 1 shows full-sided projecting elements 11 on either profile of the main filter body 12.

Figure 2 shows a profile view of another embodiment of the improved filter of the present invention. Figure 2 shows small projecting elements 11 on either profile of the main filter body 12.

Figure 3 shows a profile view of another embodiment of the improved filter of the present invention. Figure 3 shows dual projecting elements 11 on either profile of the main filter body 12.

Figures 4A and 4B show a profile view and end view respectively of another embodiment of the present invention. Figure 4A shows multiple projecting elements 11 on either side on the main filter 12, made essentially by slitting the ends of the filter 10. Figure 4B shows how the ends can look after slitting and handling as they can tend to separate and give a spring loaded effect into the "C" channel or slot holding features for the filter.

Figure 5A shows a profile view of another embodiment of the present invention. Figure 5 shows dual projecting elements 11 on either profile of the main filter body 12. These projecting elements can be of any shape and here are shown as triangular projecting elements which can adjust for any draft angle that may be molded into the disk-drive "C" channels. They also have the ability to push past and hold into any locking type feature that might be employed to hold the filter. Figure 5b shows the shaped projection element engaging a feature of the channel in a disk drive filter.

Figure 6 shows a profile view of another embodiment of the present invention. Figure 6 shows serrated or scalloped projecting elements 11 that can have any shape and be any number on both sides of the main filter 12.

Figure 7 shows an end view of another embodiment of the present invention. Figure 7 shows a three-dimensional projecting element 14 on the end of main filter element 13. The projecting element 14 adds a spring loading effect in the "C" channels by compressing or deforming the projecting element 14.

Figures 8 and 8A show profile and end views respectively of a further embodiment of the present invention. Figure 8 shows slit projecting elements 15 on the main filter body 12. Figure 8A shows an end view with the projecting elements folded over to provide the spring loading effect when pressed into the holding "C" channels.

Figure 9 shows a profile view of a further embodiment of the present invention. Figure 9 shows a single projecting element 11 on a single profile of the main filter body 12.

Figure 10 is a top view of a filter similar to the filter shown in Figure 2 installed between two "C" channels 20. The two projecting elements 11 that extend beyond the main filter body 12, are slightly bent providing the spring force to help locate and hold the filter in place.

Figures 11 A and 11 B show a top view and profile view respectively of a filter where the projecting elements 11 extend beyond the main filter body 12, and extend through slots in the "C" channels 20 to help secure the filter in place. Here the filter is more secured through the slots rather than being spring loaded into the channels. Figure 12 shows a profile view of a further embodiment of the present invention. Figure 12 shows projecting elements 15 that are overmolded onto a standard filter as a post assembly process to provide projecting elements for securing the filter into the assembly channels.

In any or all of the embodiments described and illustrated above, an adsorbent or adsorbent layers may be added to change the filter from a particle filter to a combination particle and vapor filter. The adsorbent can be treated for the adsorption of specific gaseous species such as acid gasses. The adsorbent can be disposed within the filter portion 12, and can extend into the sealed tabbed regions 11 within the assembly portion of the filter.

The adsorbent may comprise one or more layers of 100% adsorbent materials, such as granular activated carbon, or may be a filled product matrix such as a polymeric scaffold of porous polymeric material compounded with adsorbents that fill the void spaces. Other possibilities include adsorbent impregnated nonwovens or beads on a scrim where the non-woven or scrim may be cellulose or polymeric and may include latex or other binders as well as porous castings or tablets of adsorbents and fillers that are polymeric or ceramic. The adsorbent can also be a mixture of different types of adsorbents.

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

A preferred embodiment of the adsorbent layer utilizes an sorbent filled PTFE sheet wherein the sorbent particles are entrapped within the reticular PTFE structure as taught by U.S. Patent No. 4,985,296 issued to Mortimer, Jr. and specifically incorporated herein by reference. Ideally, 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 core. This technique also allows a number of sorbents to be filled into a single layer. The PTFE/adsorbent composite can easily be made in thicknesses from less than 0.001" to 0.400" and greater allowing a great deal of flexibility in finished filter thicknesses and adsorbent loading. Additionally, sorbent densities approximating 80-90% of full density are possible with multi-model packing and physical compression, so that maximum adsorbent material can be packed per unit volume. The use of PTFE as the binding element also does not block the adsorbent pores as do binders such as acrylics, melted plastic resins, etc.

The adsorbent is preferably covered with a polymeric membrane such as expanded PTFE. Using PTFE membranes as a filter material over the adsorbent layers imparts a number of additional advantages to this improved filter construction. 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 covering the carbon layer with the PTFE membrane, it makes the final part waterproof so that deionized water can come into contact with the part and not penetrate the adsorbent. 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. 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 PTFE filter layers to encapsulate the adsorbent allow use of water soluble salt treated adsorbents incorporated into the adsorbent layer and can withstand washing without loss of adsorbent treatment and effectiveness.

While these PTFE membranes are hydrophobic and can be washed, they also have a high moisture vapor transmission rate, which allows contaminants in the air to quickly and easily diffuse through the membranes into the adsorbents. They can also be made with very good filtration efficiencies which contain the carbon particles as well as filters air that passes through the material. An example of a preferred membrane for that would be one made in accordance with U. S. Patent 3,953,566. Such membranes have an efficiency of 99.97% at 0.3 microns sized particles and a permeability or face velocity of 7 feet/minute at 0.5 inches of water pressure. Such membranes are commercially available in finished filter form from W. L. Gore and Associates, Inc. Another preferred filter media to encapsulate the adsorbent layer is a layer of expanded PTFE membrane made in accordance with the teachings of U.S. Patent No. 4,902,423 to Bacino et al. incorporated by reference. This filter media has several advantages. It can be made very highly permeable, with resistances to air flow of less than 0.5 mm H2O @ 10.5 feet per minute (3.2 meters per minute) and still contain adsorbent particulate within the filter. The particle filtration efficiency of this highly expanded membrane as measured on a TSI 8160 efficiency test rig available from TSI Inc., in Minnesota, is also very good (e.g. in excess of 55% at 0.3 μm) which provides good particle filtration along with the adsorbent containment.

This filter media may optionally be structurally supported by a layer of woven, nonwoven, or expanded porous material, such as polyester, polypropylene, polyamide, etc. A preferred support layer is a Reemay 2014 polyester nonwoven, 1.0 oz/yd2 available from Reemay, Inc., Old Hickory, Tennessee.

Yet another preferred filter media to be used in both recirculation filter and adsorbent recirculation filter applications, is a layer of an electrostatic triboelectret material available in finished filter form from W. L. Gore and Associates, Inc. under the trademark GORE-TRET® recirculation filters. Advantages of this media are that it is very high in efficiency (e.g., in excess of 90% @0.3 micron) and also very permeable (e.g., less than 1 mm H₂O at 10.5 fpm or 3.2 m/min). While this media loses its charge while being washed with deionized water, it immediately regains its efficiency upon drying due to the triboelectric effect of the mix of dissimilar fibers.

Other filter materials can also be used without departing from the spirit of the invention. They could be alternative electret or other triboelectret materials that yield high efficiencies and low resistances to airflow. They could also be other filter papers or filter membranes such as polypropylene membranes or cast polymeric membranes or some combination of filter materials. These materials may be wovens, nonwovens, or expanded porous materials, such as polyester, polypropylene, polyamide, etc.

Additional functional layers may be added such as an outer protective layer or layers can also be used to add durability to the filter and to contain any protruding fibers from either the triboelectret type filter media or the filter support media for the membrane filter media. Typically, this would be an extruded or expanded plastic material such as polypropylene, polyethylene, polyamide, polyester, etc. A preferred material is a Delnet 0707 expanded polypropylene material available from DelStar Technology, Inc., Middletown, DE. Nonwoven layers may also be used for support and/or fiber containment and may be used alone in three layer constructions with the filter layer or as part of five or more layered constructions. Further layers may be added to improve various aspects of the filter, such as adsorbent layers to add adsorption performance to the filter. For example, nonwovens such as Reemay 2014 polyester nonwoven, 1.0 oz/yd2 available from Reemay, Inc., Old Hickory, Tennessee may be used as support layers or added for additional fiber containment layers.

TEST PROCEDURES

Assembly of the Device into a Modified Drive:

An example of the present invention was tested for particulate filtration performance using a commercially available 3.5 inch form factor disk drive (DiamondMax Plus 8 40GB drive from Maxtor Corporation, Milpitas, CA). None of the drive components were removed prior to modification of the drive for testing purposes. Modification consisted of drilling two holes in the drive lid to allow introduction of contaminants and sampling of the internal drive atmosphere during performance testing. Each of the holes in the lid was covered with a stainless steel fitting (Part No. SS-200-7-4, Baltimore Valve and . Fitting Co., Baltimore, MD), which was centered over the hole and attached and sealed using two component epoxy. In addition, the electrical connection to the voice coil motor (VCM) was severed in order to keep the actuator in a fixed position during all tests. The drive lid was cleaned using isopropanol and clean, pressurized air to remove any oils and particles created during modification. The head suspension assemblies were removed from the E-block prior to reassembly into the drive in order to eliminate the possibility of head crashes during testing. Following modification of the drive, the filters were mounted into the "C" channels in the drive baseplate and tested.

Disk Drive Shock test:

This test is designed to measure the effectiveness of the features of the present invention in holding the filter in the drive. The above mentioned drive was fitted with samples of a conventional filter and samples of the present invention respectively. The drive was turned over and placed on the comer of a support such that the recirculation filter was unsupported and hanging over the support. A drive top cover with a mass of approximately 166 grams was then dropped onto the back of the drive from a distance of 2 inches. The filters were observed to either drop out of the drive or remain in the drive.

Disk Drive Recirculation Filter Test:

This test is designed to measure the effectiveness of a recirculation filter in reducing the particle concentration inside a disk drive from an initial state in which the drive has been charged with particles. The performance of the recirculation filter is quantified in terms of a cleanup time, which is the time required to reduce the particle counts to a fixed percentage of their initial value.

For testing the effectiveness of the recirculation filter function the device was tested in the modified disk drive. The existing breather hole in the drive was left uncovered in order to provide a means for venting any overpressure from the drive and to allow air to enter the drive during periods when the drive environment was being sampled without air being purposefully introduced into the drive. The lid was fastened securely to the baseplate. A tube supplying an aerosol mixture of 0.1 μm and 0.3 μm particles was connected to the port in the drive lid upstream of the filter based on the direction of disk rotation. A second tube for sampling the internal atmosphere of the drive connected the laser particle counter (LPC) to the port in the drive lid downstream of the filter. Sample flow rate out of the drive and through the counter was maintained at 1 cc/sec and sheath flow through the LPC was maintained at 40 cc/sec. Counts of 0.1 μm and 0.3 μm particles were obtained once per second by the LPC and stored on a computer disk drive for later analysis. The test was performed with the drive located in a laminar flow hood fitted with a HEPA filter in the air intake, in order to maintain a controlled test environment with an extremely low ambient particle concentration. Samples of a standard sized and construction recirculation filter for this drive as supplied by W. L. Gore and Associates in Elkton, Md was tested as well as a similar filter but designed as Figure 2 where two small 0.040" projecting elements were added to each end of the filter. The filter appeared similar to Figure 10 when installed into the drive. A control drive, of the same model and also having had its head suspension assemblies removed, contained no recirculation filter. The recirculation filter test consisted of the following sequence: With the drive powered on and clean air passing through the drive, the counts of 0.1 μm and 0.3 μm particles were monitored until a low background count was achieved, typically when 0.3 μm particles were less than 3 counts per second and 0.1 μm particles were less than 10 counts per second. At that time the aerosol was flowed into the drive in order to charge the internal environment with particles. When fully charged and stabilized, counts of 0.1 μm particles were typically between 5000 and 10000 per second and counts of 0.3 μm particles were typically between 3000 and 6500 per second. At this point the flow of aerosol into the drive was halted while sampling of the internal drive atmosphere continued, by drawing out of the drive air which entered through the open breather hole in the baseplate as well as any leaks in the lid or baseplate. The concentration of 0.1 μm and 0.3 μm particles were observed to drop over time. This drop was due to the recirculation of air through the drive and the filter, impaction of the particles on surfaces inside the drive, and the gradual exchange of particle-laden sample air with clean make-up air drawn in through the breather hole. Monitoring of the drive continued until the particle counts dropped to the initial background values observed prior to charging the drive with aerosol.

The data was analyzed by measuring the time required for the counts of 0.1 μm and 0.3 μm particles to fall to 0.1% of their value when the drive was fully charged with particles, defined as the cleanup time or t₉₉ or 99% cleaned up. Three individual tests were performed in order to check reproducibility and eliminate error from noise in the background counts. The results from the three tests were averaged to obtain the average cleanup times for 0.1 μm and 0.3 μm particles. Again, results reported are for 0.1 micron particles unless otherwise noted. Further analysis can calculate a RCUR time by dividing the t₉₉ time of the filter by the t₉₉ time of the no filter run to get a number referred to as the RCUR number or Relative Clean-Up Ratio.

Without intending to limit the scope of the present invention, the following examples illustrate how the present invention may be made and used.

A 3.5" computer hard disk drive was modified as stated above for testing particle clean-up in a modified drive where inlet and outlet ports were mounted to the lid of the hard drive. The samples were tested in accordance to the procedures previously outlined. Example 1

Samples were made up to test the recirculation filter functionality of a recirculation filter with and without projecting elements and without any adsorbents. The conventional filter without projecting elements was a standard filter for the drive as supplied by W. L. Gore and Associates, Elkton MD. The conventional filter had length and width dimensions of 13mm by 7 mm. An inventive filter similar to that as shown in Figure 2 was also made. The inventive filter included a filter portion that was 0.040" shorter in overall length than the conventional filter and had a small projecting element extending 0.040" from each end of the filter. The filter with projecting elements was constructed of the same material set as the conventional filter. They were five layer constructions with outer layers of previously described Delnet 0707, inner layers of a Reemay nonwoven around a center layer of electret filter material all as supplied in finished filter form by W. L. Gore and Associates. . A no-filter test was also run as a control. The results are plotted in Chart 1 , and tabulated in Table 1. The results show the filter lost no performance.

Chart 1

Standard Recirc Vs Recirc With Tabs @ 0.3 microns

Rep 1 2 Rep 1 Rep 2

Table 1

The disk drive shock test was performed on ten different filters for each of the conventional filters and the present inventive filters. The filters were inserted into the c-channels in the drive and shocked as described above. All ten of the conventional filters fell out of the channels and dropped onto the floor, either when the drive was initially turned over (before impact) or when the cover was dropped onto the back of the drive. All ten of the inventive recirc filters remained in place during both turning the drive over and dropping the cover onto the back of the drive. 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

CLAIMSWe claim:

1. A filter assembly for mounting in a channel within a disk drive enclosure, the filter assembly comprising: a) a filter having at least a first end comprising a first linear edge and a second end opposite the first end, the second end comprising a second linear edge, said filter having a length equal to the minimum distance between the first linear edge and the second linear edge; and b) at least one flexible projecting element extending from at least one of the first linear edge and the second linear edge for an orthogonal distance equal to at least 0.005" (0.127 mm).

2. The filter assembly of claim 1, in which said flexible projecting element extends from the first linear edge An orthogonal distance of at least about 0.020" (0.5 mm).

3. The filter assembly of claim 1, in which said flexible projecting element extends from the first linear edge an orthogonal distance of at least about 0.040" (1 mm).

4. The filter assembly of claim 1 , wherein said flexible projecting element deforms when inserted in the channel.

5. A disk drive enclosure having a filter assembly mounted in a channel, the channel having two bearing surfaces spaced apart to form a channel having a width, the filter assembly comprising: a) a filter portion having at least a first end comprising a first linear edge and a second end opposite the first end, the second end comprising a second linear edge, said filter portion having a length equal to the minimum distance between the first linear edge and the second linear edge.

b) an assembly portion comprising at least one flexible projecting element extending from at least one of the first linear edge of said filtering portion and the second linear edge, said at least one flexible projecting element contacting the bearing surface of the channel and being deformed thereby, wherein the length of the filter assembly is greater than the channel width.

6. A disk drive filter assembly comprising: a) a layered construction comprising at least one electret filter layer comprising fibrous electret material, disposed between a first and second polyester non-woven filter layer, a first support layer adjacent to the first polyester non-woven filter layer and a second support layer adjacent to the second polyester non-woven filter layer, said first and second support layer comprising polyethylene screen material; b) a sealed edge at the perimeter of said layered construction, the sealed edge forming a substantially rectangular filter assembly having at least a first and second substantially parallel sealed edges, the filter assembly having a length equal to the distance between the first and second sealed edges, and c) at least one flexible projecting element projecting outwardly from at least one of the first sealed edge and the second sealed edge for an orthogonal distance of at least 0.005" (0.127 mm).

7. A disk drive filter assembly comprising: a. a layered construction comprising at least one filter layer comprising fibrous material, disposed between a first and second functional layer. b. a sealed edge at the perimeter of said layered construction, the sealed edge forming a substantially rectangular filter assembly having at least a first and second substantially parallel sealed edges, the filter assembly having a length equal to the distance between the first and second sealed edges, and c. At least one projecting element projecting outwardly or inwardly from at least one of the first sealed edge and the second sealed edge for a distance of at least 0.005" (0.127 mm)

8. The filter assembly of claim 7, in which said projecting element extends from at least one of the said first sealed edge and the second sealed edge for a distance of at least 0.020" (0.5 mm)

9. The filter assembly of claim 7, in which said projecting element extends from at least one of the said first sealed edge and the second sealed edge for a distance of at least 0.040" (1 mm)

10. The filter assembly of claim 1 , further comprising an adsorbent layer located in laminar relation to the filter layer.

11. The filter assembly of claim 1 , wherein said filter assembly further comprises an electret or triboelectret material.

12. The filter assembly of claim 1 , wherein the filter layer is selected from polypropylene of a mixture of polypropylene and acrylic or modified acrylic.

13. The filter assembly of claim 1 , wherein said filter assembly further comprises an adsorbent layer.

14. The filter assembly of claim 13, wherein the adsorbent layer is a physiosorber made of a material selected from the group consisting of silica gel, activated carbon, activated alumina, molecular sieves, clays, and adsorbent polymers.

15. The filter assembly of claim 13, wherein the adsorbent layer contains a chemisorbent selected from the group consisting of calcium carbonate, calcium sulfate, potassium carbonate, potassium permanganate, sodium carbonate, sodium phosphate and activated metals.

16. The filter assembly of claim 13, wherein the adsorbent layer is a polymeric scaffold that is impregnated with an adsorbent.

17. The filter assembly of claim 16, wherein the polymeric scaffold is selected from the group consisting of membranes of polypropylene, polyethylene, polyvinylidene fluoride, polyvinyl alcohol and polyethylene terepthalate.

18. The filter assembly of claim 16, wherein the scaffold is polytetrafluoroethylene or expanded polytetrafluoroethylene.

19. The filter assembly of claim 1 , wherein the projecting element is fastened to the filter with adhesive.

20. The filter assembly of claim 1 , wherein said at least one flexible projecting element is made by overmolding a moldable material onto a filter.

21. The filter assembly of claim 1 , wherein the channel includes a feature and the projecting element engages said feature of the channel to lock can lock into a locking filter in place.