Patent Grant
6858297
This invention pertains to fibrous filtration webs and a method of making such webs where the webs exhibit fiber alignment in the machine direction and have lengths of 1 to 10 centimeters.
Meltblown nonwoven fibrous webs are used for a variety of purposes including filtration (e.g., flat web and pleated filters), insulation, padding and textile substitutes. References relating to meltblown nonwoven fibrous webs include U.S. Pat. No. 3,959,421 (Weber et al.), U.S. Pat. No. 4,622,259 (McAmish et al.), U.S. Pat. No. 5,075,068 (Milligan et al.), U.S. Pat. No. 5,141,699 (Meyer et al.), U.S. Pat. No. 5,405,559 (Shambaugh), U.S. Pat. No. 5,652,048 (Haynes et al.), U.S. Pat. No. 5,665,278 (Allen et al.), U.S. Pat. No. 5,667,749 (Lau et al.), U.S. Pat. No. 5,772,948 (Chenoweth) and U.S. Pat. No. 5,811,178 (Adam et al.). References relating to pleated filters include U.S. Pat. No. 4,547,950 (Thompson), U.S. Pat. No. 5,240,479 (Bachinski), U.S. Pat. No. 5,709,735 (Midkiff et al.), U.S. Pat. No. 5,820,645 (Murphy, Jr.) and U.S. Pat. No. 6,521,011 B1 (Sundet et al. '011), and U.S. Patent Application Publication Nos. US 2003/0089090 A1 (Sundet et al. '090) and US 2003/0089091 A1 (Sundet et al. '091).
Nonwoven web manufacture typically involves deposition of fibers on a moving collector surface. Perhaps partly as a consequence of this motion, the collected web may exhibit a small degree of fiber alignment in the machine direction, and to a small extent some anisotropic physical properties (e.g., tensile strength) in the machine and transverse directions. Nonwoven web manufacturers often strive however to make products having well-balanced and generally isotropic physical properties.
We have found that by forming nonwoven webs having much greater than normal fiber alignment in the machine direction, we can obtain webs with improved mechanical properties or improved filtration performance. The resultant webs are particularly useful for forming pleated filtration media having pleats generally transverse to the machine direction. The present invention provides, in one aspect, a method for forming a fibrous filtration web comprising:
In another aspect, the invention provides a fibrous filtration material in the form of a web having an elongate lengthwise dimension corresponding to a direction of web formation and a narrow widthwise dimension transverse to the lengthwise dimension, the web comprising nonwoven thermoplastic fibers a majority of which are aligned within ±20° of the direction of web formation, and wherein in a web that has not been heat treated, fibers having lengths of about 1 to about 10 cm can be teased from the web.
These and other aspects of the invention will be apparent from the detailed description below. In no event, however, should the above summaries be construed as limitations on the claimed subject matter, which subject matter is defined solely by the attached claims, as may be amended during prosecution.
Like reference symbols in the various figures of the drawing indicate like elements. The elements in the drawing are not to scale.
The phrase “nonwoven web” refers to a fibrous web characterized by entanglement or point bonding of the fibers.
The phrase “filtration web” refers to a porous web capable of removing at least particles having an average particle diameter greater than 10 μm from a stream of air flowing at a 0.5 m/sec face velocity at an initial pressure drop no greater than about 50 mm H2O.
The phrase “attenuating the filaments into fibers” refers to the conversion of a segment of a filament into a segment of greater length and smaller diameter.
The word “meltblowing” refers to a method for forming a nonwoven web by extruding a fiber-forming material through a plurality of orifices to form filaments while contacting the filaments with air or other attenuating fluid to attenuate the filaments into fibers and thereafter collecting a layer of the attenuated fibers.
The phrase “meltblown web” refers to a nonwoven web made using meltblowing.
The phrase “nonwoven die” refers to a die for use in meltblowing.
The phrases “meltblown fibers” and “blown microfibers” refer to fibers made using meltblowing.
The phrase “machine direction” when used with respect to a meltblown web or to a meltblowing apparatus for meltblown web formation refers to the in-plane direction of web fabrication.
The phrase “transverse direction” when used with respect to a meltblowing apparatus or a meltblown web refers to the in-plane direction perpendicular to the machine direction.
The phrase “row direction” when used with respect to a pleated filter element refers to a direction generally parallel to the pleat ridges and valleys in a filter element having a folded structure with parallel, generally sharp-edged creases, and to a direction generally parallel to the pleat crowns and base regions in a filter element having a corrugated structure with parallel, generally smooth undulations.
The term “self-supporting” when used with respect to a web refers to a web having sufficient coherency and strength so as to be drapable and handleable without substantial tearing or rupture, and when used with respect to a pleated filter refers to a filter whose pleats have sufficient stiffness so that they do not collapse or bow excessively when subjected to the air pressure typically encountered in forced air ventilation systems.
A variety of polymers may be employed to make the disclosed aligned fiber webs. Representative polymers are thermoplastic, extrudable and can be processed using a meltblowing apparatus, and include polyolefins such as polyethylene, polypropylene or polybutylene; polyamides; polyesters such as polyethylene terephthalate; and other materials that will be familiar to those skilled in the art. Polyolefins are particularly preferred.
A variety of sorbent particles can be added to the nonwoven webs if desired. Representative sorbent particles are disclosed in U.S. Pat. No. 3,971,373 to Braun, U.S. Pat. No. 4,429,001 to Kolpin et al. and U.S. Pat. No. 6,102,039 to Springett et al. Activated carbon and alumina are particularly preferred sorbent particles. Mixtures of sorbent particles can be employed, e.g., to absorb mixtures of gases, although in practice to deal with mixtures of gases it may be better to fabricate a multilayer pleated filter employing separate sorbent particles in the individual layers. If employed, preferably at least 80 weight percent sorbent particles, more preferably at least 84 weight percent sorbent particles and most preferably at least 90 weight percent sorbent particles are enmeshed in the web.
A variety of primary and secondary fluid streams may be employed in the invention. Air is an especially convenient fluid for both purposes. The remainder of this application will discuss the use of air, sometimes referred to as “primary air” or as “secondary quench air” as the context may require. Those skilled in the art can readily employ other fluids (e.g., carbon dioxide, nitrogen or water) with appropriate modification of the operating parameters described below.
Viewed from the side (or transverse direction) using high-speed photography, fibers 24 are laid down on collector 26 in a “paintbrush” fashion. Measured at the collector, the oscillations can have a very large machine direction amplitude, e.g., more than one fourth the die to collector distance (“DCD”) and in some instances more than half the DCD. Several operating conditions may be especially desirable to achieve such paintbrush deposition. For example, the oscillations may occur regularly, may have increasing amplitude en route to the collector, and may have a wavelength for one complete cycle that is less than the distance from the secondary quench air outlets to the collector. Preferably the distance from the secondary quench air outlets to the collector is not overly long. The fibers may in some instances exhibit a whip-like action at their peak machine direction displacement en route to the collector, and may momentarily move towards the meltblowing die rather than always moving toward the collector. Apparent fiber breakage can sometimes be seen as such whip-like action occurs.
We have been able to tease fibers with discrete lengths (e.g., between about 1 and about 10 cm, along with occasional shorter or longer fibers) from the collected webs using tweezers. Ordinarily it is quite difficult to remove any fibers (or any fibers of such lengths) from conventional nonwoven webs, as the fibers typically are restrained in the web by fiber-to-fiber bonding or by interfiber entanglement.
Web 28 can be used as is, or further treated. For example, heat treatments (e.g., annealing, using equipment not shown in
A vacuum can optionally be drawn thorough orifice 34 to assist in consolidating web 28. Overdensification (e.g., using calendaring) may however destroy the web's filtration capability. Electric charge can be imparted to the fibers by contacting them with water as disclosed in U.S. Pat. No. 5,496,507 to Angadjivand et al., corona-treating as disclosed in U.S. Pat. No. 4,588,537 to Klasse et al., hydrocharging as disclosed, for example, in U.S. Pat. No. 5,908,598 to Rousseau et al. or tribocharging as disclosed in U.S. Pat. No. 4,798,850 to Brown. Additives may also be included in the fibers to enhance the web's filtration performance, mechanical properties, aging properties, surface properties or other characteristics of interest. Representative additives include fillers, nucleating agents (e.g., MILLAD™ 3988 dibenzylidene sorbitol, commercially available from Milliken Chemical), UV stabilizers (e.g., CHIMASSORB™ 944 hindered amine light stabilizer, commercially available from Ciba Specialty Chemicals), cure initiators, stiffening agents (e.g., poly(4-methyl-1-pentene)), surface active agents and surface treatments (e.g., fluorine atom treatments to improve filtration performance in an oily mist environment as described in U.S. Pat. Nos. 6,398,847 B1, 6,397,458 B1, and 6,409,806 B1 to Jones et al.). The types and amounts of such additives will be apparent to those skilled in the art.
The completed webs may have a variety of effective fiber diameter (“EFD”) sizes, basis weights and solidity (ratio of polymer volume to web volume) values. Preferred EFDs are about 3 to about 25 μm for flat blown microfiber (“BMF”) filtration layers (more preferably about 7 to about 25 μm), and about 10 to about 25 μm for BMF pleated filters. Preferred basis weights are about 15 to 100 g/m2 for flat BMF filtration layers, and about 50 to about 100 g/m2 for BMF pleated filters. Preferred solidity values are about 5 to about 15% for flat BMF filtration layers or BMF pleated filters.
The disclosed webs have substantial machine direction (direction of motion or direction of web formation) fiber alignment. As a general guide for use with webs made from polypropylene, preferably about 55 to about 90% of the fibers are aligned within ±20° of the direction of motion, and more preferably about 70 to about 85%. For webs made from other polymeric materials the numbers may be lower or higher. For example, as a general guide for webs made from polyethylene terephthalate, preferably about 51 to about 80% of the fibers are aligned within ±20° of the direction of motion, and more preferably about 60 to about 80%. As a general guide for webs made from nylon, preferably about 51 to about 70% of the fibers are aligned within ±20° of the direction of motion. Very highly aligned webs can be formed, e.g., webs having at least 80% of the collected fibers aligned within ±10° of the direction of motion.
The disclosed webs have one or more anisotropic mechanical properties. One class of preferred webs may have at least a 2:1 ratio of the in-plane direction of motion tensile strength to transverse direction of motion tensile strength using a 50 mm gauge length, and more preferably at least a 3:1 ratio. Another class of preferred webs may have at least a 2:1 ratio of the in-plane direction of motion Taber Stiffness to transverse direction of motion Taber Stiffness, and more preferably at least about 2.2:1.
It is possible to construct the disclosed apparatus and operate it under conditions that do not provide the disclosed aligned fiber webs, or under conditions that will provide weak webs poorly suited to filtration. For example, if insufficient secondary quench air is employed then the above-described oscillations may not occur and the fibers may not align substantially in the machine direction. Excessively high quench velocities may provide loftier webs having less interfiber bonding and entanglement and improved filtration performance, but having severely diminished mechanical properties such as stiffness and pleatability. Thus it generally will be preferable to employ secondary quench air within a range of mass flow ratios or volumes. As an example for webs made using polypropylene and secondary air chilled to below ambient temperature, a ratio of about 500 to about 2000 grams of secondary quench air per gram of extruded polymer may be preferred, as may be secondary quench air outlet velocities of about 15 to about 60 m/sec. These ranges may need to be adjusted empirically based on factors such as the meltblowing die and polymer employed, the target basis weight, target web solidity and target extent of fiber alignment and mechanical property anisotropy. Pulsation of the secondary quench air may also be employed but appears not to be necessary. Instead it appears to be better simply to adjust the secondary quench air flow upwards or downwards to a steady state value that provides collected webs having the desired final properties.
Further details regarding the manner in which meltblowing would be carried out using an apparatus like that shown in FIG. 1 and
The fibrous filtration webs can be further stiffened if desired using a variety of techniques. For example, an adhesive can be employed to laminate together layers of the web, e.g., as described in U.S. Pat. No. 5,240,479 (Bachinski). The web can also be made using conjugate fibers, e.g., as described in U.S. Pat. No. 5,709,735 (Midkiff et al.).
The fibrous filtration webs may be employed in a variety of applications including ventilation (e.g., furnace and clean room filters), pollution control (e.g., baghouse filters), liquid treatment (e.g., water filters), personal protection (e.g., filtering face masks), chemical or biological analysis (e.g., affinity membranes), medical devices (e.g., dialysis equipment) and other applications that will be familiar to those skilled in the art. Pleated filter media is an especially preferred application. For example,
The invention will now be described with reference to the following non-limiting examples, in which all parts and percentages are by weight unless otherwise indicated. Several measurements were carried out as follows:
Effective geometric fiber diameters were evaluated according to the method set forth in Davies, C. N., “The Separation of Airborne Dust and Particles,” Institution of Mechanical Engineers, London, Proceedings 1B, 1952.
The overall visual web appearance was evaluated using a Zeiss Instruments dissecting microscope equipped with a charge coupled device camera having an 8 mm×14 mm magnification window.
Web stiffness was evaluated using a Model 150-B TABER™ stiffness tester (commercially available from Taber Industries). Square 3.8 cm×3.8 cm sections were carefully vivisected from the webs using a sharp razor blade to prevent fiber fusion, and evaluated to determine their stiffness in the machine and transverse directions using 3 to 4 samples and a 15° sample deflection.
Stress-strain (or load vs. elongation) was measured using a Model 5544 INSTRON™ universal testing machine (commercially available from Instron Corp.). Rectangular 2.5 cm×6.3 cm sections were cut from the webs using a sharp razor blade and evaluated to determine the maximum force and elongation at maximum force, using 6 to 10 samples, a 50 mm initial jaw separation and a 3 cm/min stretch rate.
Filtration quality factors (QF) were determined using a TSI™ Model 8130 high-speed automated filter tester (commercially available from TSI Inc.) and a dioctyl phthalate (“DOP”) challenge aerosol flowing at 42.5 L/min. Calibrated photometers were employed at the filter inlet and outlet to measure the DOP concentration and the % DOP penetration through the filter. An MKS pressure transducer (commercially available from MKS instruments) was employed to measure pressure drop (ΔP, mm H2O) through the filter. The equation:
was used to calculate QF. QF values can be reported as a curve plotting QF vs. the DOP challenge total mass after various time periods. However, the initial QF value usually provides a reliable indicator of overall performance, with higher initial QF values indicating better filtration performance and lower initial QF values indicating reduced filtration performance. Initial filtration quality factors QF of at least about 0.6 (using 100 ppm dioctyl phthalate particles having a size range between 10 and 700 nm traveling at a 7 cm/sec face velocity), more preferably at least about 0.8 and most preferably at least about 1 are preferred.
Filtration performance was evaluated according to ASHRAE standard 52.2, “Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size”. The ASHRAE standard evaluates filtration of a test aerosol containing laboratory-generated potassium chloride particles dispersed into an airstream. A particle counter measures and counts the particles in 12 size ranges upstream and downstream from the filter. The results can be reported as minimum composite efficiency values for particles in various size ranges. The minimum composite efficiency values correspond to the minimum percent particle retention (the downstream particle count/upstream particle count×100 for the size range in question) as the filter is loaded to a final pressure drop of 25.4 mm H2O. A set of particle size removal efficiency (PSE) performance curves at incremental dust loading levels may also be developed, and together with an initial clean performance curve may be used to form a composite curve representing the minimum performance in each size range. Points on the composite curve are averaged and the averages used to determine the minimum efficiency reporting value (MERV) for the filter.
A conventional 20.5 cm wide meltblowing apparatus was modified by addition of a secondary air quench system and a flat-bed collector arranged as in FIG. 1. In a conventional blown microfiber process, secondary quench air would not be employed and the web would be collected on a rounded surface such as a porous drum. The modified apparatus was used to make meltblown polypropylene webs whose fibers were highly aligned in the machine direction. The secondary air quench system employed two opposed horizontally-disposed 76 cm wide×51 cm high air outlets disposed approximately 6 cm below the meltblowing die tip, dispensing 12-13° C. chilled air flowing at various rates (or not at all) through the air outlets. The flat-bed collector employed a vacuum collection system located under the bed. The meltblowing die was positioned over the leading edge of the collector. FINA™ type 3960 polypropylene (commercially available from Fina Oil and Chemical Co.) was melted in an extruder operated at 265° C. and fed at 9.1 kg/hr to the meltblowing die. The die was maintained at about 265° C. using resistance heaters and supplied with 300° C. primary air flowing at 4.2 m3/min. The DCD was adjusted to provide webs having a 0.5 mm H2O pressure drop at a 32.5 L/min flow rate. For webs prepared using secondary quench air, the DCD was approximately 20 cm. For webs prepared without secondary quench air, the DCD was approximately 34 cm. The collector vacuum was adjusted to provide webs having 8-9% solidity. The collector vacuum was 3250 N/m2 for webs prepared using secondary quench air at 50 or 35 m/sec outlet velocity, 5000 N/m2 for webs prepared using secondary quench air at 17 m/sec outlet velocity, and zero for webs prepared without secondary quench air. The collected webs had an 80 g/m2 basis weight and a 19 μm EFD. The webs were corona-treated as described in U.S. Pat. No. 4,588,537 to Klasse et al., hydrocharged as described in U.S. Pat. No. 5,908,598 to Rousseau et al. and evaluated to determine their mechanical properties and filtration quality factor QF. The webs were also heat treated at 126° C. for 5 minutes and reevaluated to determine their mechanical properties.
Set out below in Table 1 are the Example No. or Comparison Example No., secondary air velocity and mass flow ratio, the fiber count and fiber alignment data, and the filtration quality factor QF for each web. Set out below in Table 2 are the machine direction (“MD”) and transverse direction (“TD”) Taber Stiffness and tensile strength values for the each web, and the ratio of MD to TD Taber Stiffness and tensile strength. Set out below in Table 3 are the MD and TD Taber Stiffness and tensile strength values for the heat treated webs, and the ratio of MD to TD Taber Stiffness and tensile strength.
As shown in Table 1, webs made using secondary quench air had significantly greater machine direction fiber alignment than webs made without secondary quench air. This is further illustrated in
The
Table 1 also shows that as the secondary quench air volume increased, the filtration quality factor QF increased and then decreased slightly.
Webs prepared using secondary air had visible striations generally aligned in the machine direction, a surface with an overall smooth sheen and slight fuzziness, and few or none of the nodules that usually are found in conventional blown microfiber webs. Fibers having approximately 2 to 5 cm lengths could be teased from the webs using tweezers. Webs prepared without secondary quench air visually resembled standard blown microfiber webs collected on a round collector. Some relatively short (less than 1 cm) individual fibers could be removed from these webs using tweezers, but only with great difficulty.
As shown in Table 2, webs made using secondary quench air had significantly more anisotropic Taber Stiffness than webs made without secondary quench air. Webs made using higher volumes of secondary quench air also had significantly more anisotropic tensile strength than webs made without secondary quench air.
As shown in Table 3, heat treating could be used to increase web stiffness and tensile strength. For several of the webs this could be done without causing a substantial change in the web's overall mechanical anisotropy as measured using MD:TD property ratios.
Using the general method of Example 1, meltblown polypropylene webs were prepared using 300° C. primary air flowing at 3.4 m3/min and secondary quench air and collector vacuum adjusted to provide collected webs having an 80 g/m2 basis weight, 8-9% solidity and smaller effective fiber diameters than were obtained in Example 1. Set out below in Table 4 are the Example No., secondary air velocity and mass flow ratio, effective fiber diameter and the fiber count and fiber alignment data for the resulting webs.
As shown in Table 4, webs having substantial machine direction fiber alignment could be made at a variety of effective fiber diameters.
Using the general method of Example 1, polyethylene terephthalate (“PET”) and nylon (ULTRAMID™ BS-400N nylon, commercially available from BASF Corp.), were employed to prepare nonwoven webs using 350° C. primary air flowing at 2.9 m3/min and optional secondary quench air. A 12.7 cm DCD was used to prepare the PET webs and a 16.5 cm DCD was used to prepare the nylon webs. The collected PET webs had an 85 g/m2 basis weight, 5-6% solidity and a 16 μm EFD. The collected nylon webs had a 70 g/m2 basis weight, 5-6% solidity and a 17-18 μm EFD. Set out below in Table 5 are the Example No. or Comparison Example No., secondary air velocity and mass flow ratio, polymer employed and the fiber count and fiber alignment data for the resulting webs.
As shown in Table 5, webs having substantial machine direction fiber alignment could be made using a variety of polymers.
Example 2 was repeated using a 1.5% addition of the additive poly(4-methyl-1-pentene). This increased the filtration quality factor QF from 1.5 without the additive to 1.7 with the additive.
Example 11 was repeated using a 1.5% addition of the additive poly(4-methyl-1-pentene) and a 0.5% addition of CHIMASSORB 944 hindered amine light stabilizer. The web was hydrocharged but not corona-treated. The filtration quality factor QF was 2.5, and more than double that obtained using webs made from conventional untreated polypropylene blown microfibers made without secondary quench air.
Using the general method of Example 1, meltblown polypropylene webs were prepared with and without secondary quench air flowing at a 1770 secondary quench air:polymer mass flow ratio, corona-treated, hydrocharged, and evaluated to determine their filtration quality factor QF. The webs had an 85 g/m2 basis weight, 19-21 μm EFD, and a pressure drop of 0.4-0.5 mm H2O at 42.5 L/min. Set out below in Table 6 are the QF factors after various cumulative DOP exposure levels for the web made with (Example 13) or without (Comparison Example 4) secondary quench air.
As shown in Table 6, a web made using secondary quench air and having substantial machine direction fiber alignment provided significantly better filtration performance than a web made without secondary quench air and having less fiber alignment.
The corona-treated and hydrocharged Example 2 webs, the corona-treated and hydrocharged Comparison Example 1 webs and a sample of ACCUAIR™ corona-treated spunbond polyethylene/polypropylene twinned fiber web (71 g/m2 basis weight, ˜20 μm EFD, commercially available from Kimberly Clark Corp.) were formed into 50.8 cm×63.5 cm×2.1 cm filter elements having pleats 102 like pleated media 100 shown in FIG. 7. The pleats 102 were arranged so that the folds were aligned with the transverse direction, with 87 pleats (13.8 pleats/10 cm) along the long dimension. The pleated media 100 was sandwiched between and glued to expanded metal supports like support 110 and mounted in a cardboard frame like frame 112 shown in
As shown in Table 7, corona-treated or corona-treated and hydrocharged meltblown nonwoven webs made using secondary quench air and having substantial machine direction fiber alignment (Examples 14 and 15) provided much better minimum composite efficiency at a 1 mm H2O pressure drop than otherwise similar meltblown nonwoven webs made without secondary quench air and having less fiber alignment (Comparison Examples 5 and 6). The Example 14 and Example 15 webs also had comparable or better minimum composite efficiency than a commercial spunbond nonwoven web (Comparison Example 7). The Example 14 and Example 15 webs had better particle capture (as evidenced by their higher total filter weight gain values) than the Comparison Example 5-7 webs.
Using the general method of Examples 14 and 15, a meltblown aligned fiber polypropylene web was corona-treated and hydrocharged but not heat treated. This web had a 1.7 MD Taber Stiffness value and is identified below as the web of Example 16. A stiffer web was prepared using corona-treatment, hydrocharging and heat treatment. This web had a 2.2 MD Taber Stiffness value and is identified below as the web of Example 17. A yet stiffer web was prepared using a 1.5% addition of the additive poly(4-methyl-1-pentene), corona-treatment, hydrocharging and heat treatment. This web had a 3.7 MD Taber Stiffness value and is identified below as the web of Example 18. The Example 16-18 webs and a sample of ACCUAIR corona-treated spunbond polyethylene/polypropylene twinned fiber web (having a 2.1 MD Taber Stiffness and identified below as the web of Comparison Example 8) were formed into 30 cm×27 cm×2.1 cm high filter elements having pleats 102 like filter media 100 shown in FIG. 7. The filters had 13.8 pleats/10 cm along the long dimension, and were sandwiched between and glued to expanded metal supports like support 110 in FIG. 8. In a series of runs, each such filter was mounted in a PLEXIGLAS™ plastic frame whose transparent side plates permitted the pleat edges to be photographed. The frame side plates touched the filtration media edges but permitted pleat movement. The frame was mounted atop a vacuum table and exposed to air from a downwardly-directed box fan. The filters were loaded by sprinkling a synthetic dust made from a 50:50 mixture of SAE Fine Test Dust and talc into the air stream until the filter pressure drop reached about 0.35 in (0.9 cm) of water at an approximate 1.5 m/sec face velocity. This simulated a substantial natural loading level. Set out below in Table 8 are the filter descriptions, MD Taber Stiffness values and total filter weight gain values.
The filters were next mounted in a duct equipped with an anemometer and exposed to flowing air at velocities sufficient to cause pressure drops between about 0.2 in. (0.5 cm) of water and 1.2 in. (3 cm) of water. The Example 16 (1.7 MD Taber Stiffness) filter began to exhibit noticeable pleat deformation, manifested by pinching together of the pleats at the filter air inlet side, at a 0.35 in (0.9 cm) pressure drop. The Example 17 (2.2 MD Taber Stiffness) and Comparison Example 8 filters began to exhibit noticeable pleat deformation at a 0.5 in (1.3 cm) pressure drop. The Example 18 (3.7 MD Taber Stiffness) filter did not exhibit noticeable pleat deformation even at a 1.2 in (3 cm) pressure drop.
Various modifications and alterations of this invention will be apparent to those skilled in the art without departing from this invention. This invention should not be restricted to that which has been set forth herein only for illustrative purposes.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3959421 | Weber et al. | May 1976 | A |
| 3971373 | Braun | Jul 1976 | A |
| 4429001 | Kolpin et al. | Jan 1984 | A |
| 4547950 | Thompson | Oct 1985 | A |
| 4588537 | Klasse et al. | May 1986 | A |
| 4622259 | McAmish et al. | Nov 1986 | A |
| 4798575 | Siversson | Jan 1989 | A |
| 4798850 | Brown | Jan 1989 | A |
| 4976677 | Siversson | Dec 1990 | A |
| 5075068 | Milligan et al. | Dec 1991 | A |
| 5141699 | Meyer et al. | Aug 1992 | A |
| 5240479 | Bachinski | Aug 1993 | A |
| 5389175 | Wenz | Feb 1995 | A |
| 5405559 | Shaunbaugh | Apr 1995 | A |
| 5496507 | Angadjivand et al. | Mar 1996 | A |
| 5652048 | Haynes et al. | Jul 1997 | A |
| 5665278 | Allen et al. | Sep 1997 | A |
| 5667749 | Lau et al. | Sep 1997 | A |
| 5709735 | Midkiff et al. | Jan 1998 | A |
| 5772948 | Chenowith | Jun 1998 | A |
| 5782944 | Justice | Jul 1998 | A |
| 5811178 | Adam et al. | Sep 1998 | A |
| 5820645 | Murphy, Jr. | Oct 1998 | A |
| 5908598 | Rousseau et al. | Jun 1999 | A |
| 6102039 | Springett et al. | Aug 2000 | A |
| D449100 | Sundet et al. | Oct 2001 | S |
| 6397458 | Jones et al. | Jun 2002 | B1 |
| 6398847 | Jones et al. | Jun 2002 | B1 |
| 6409806 | Jones et al. | Jun 2002 | B1 |
| 6521011 | Sundet et al. | Feb 2003 | B1 |
| 20030089090 | Sundet et al. | May 2003 | A1 |
| 20030089091 | Sundet et al. | May 2003 | A1 |
