MXPA98008570A - Fabrics for cleaner with vacuum united by hil - Google Patents

Abstract

A filter means for vacuum cleaner is provided which is a fabric bonded by non-woven yarn of conjugated spunbonded fibers. The fabric has a frazier permeability of at least 250 CFM, an NaCl efficiency of at least 65%, and a Gurley stiffness of at least 20 mg, and a pressure drop of 0.5 or less mm H2O. The conjugated fibers are made of polymers, more particularly of polyolefins, even more particularly of polypropylene and polyethylene in a side-by-side configuration. The filter medium is treated with a hot air knife and is bonded through air during the production process. The medium is also treated with an electrode. The medium has sufficient stiffness to become a filter through conventional means. While this invention is directed primarily to the purification and filtration of air, other gases can also be filtered.

Description

FABRICS FOR CLEANER WITH VACUUM UNITED BY YARN BACKGROUND OF THE INVENTION This invention relates generally to a non-woven fabric which is formed of fibers joined by spinning a thermoplastic resin and laminates using such a fabric as a component. The fabric has a particular applicability in vacuum cleaning since it provides a low pressure drop and good filtering efficiency.

Thermoplastic resins have been extruded to form fibers and fabrics for several years. The most common thermoplastics for this application are polyolefins, particularly polypropylene. Other materials such as polyester, polyether esters, polyamides and polyurethanes are also used to form non-woven spunbonded fabrics.

Non-woven fabrics are useful for a wide variety of applications such as diaper components, women's hygiene products, towels, protective and recreational fabrics and as geotextiles and filter media. The non-woven fabrics used in these applications can be simply spun-bonded fabrics but are often in the form of non-woven fabric laminates such as spin-bonded / spin-bonded (SS) laminates or spin-bonded / melt-bonded laminates / joined by spinning (SMS).

Vacuum bags require high permeability in order to produce the lowest possible back pressure against the blower motor but also require good filtering efficiency. Previous attempts to provide a high efficiency vacuum bag have generally focused on paper, co-melt blown fabrics and filter cloth laminates and a backing layer.

U.S. Patent No. 4,589,894 issued to Gin et al. For a Disposable Filter for a Vacuum Cleaner shows an inner layer of microfibers, such as meltblown fibers and highly porous outer support layers on either side of the cap. interior wherein the highly porous support layers are woven preferably by spinning.

The United States patent of North America No. 4,917,942 issued to Winters shows a laminate of a cap containing microfiber electret, preferably meltblown, and a support layer of a highly permeable fabric, preferably spunbond. The laminate is suitable for use in vacuum cleaner bags.

U.S. Patent No. 5,080,702 issued to Bosses shows a two-layer vacuum bag comprising a blown layer with internal fusion highly permeable to air and a conventional outer layer which can be made of wood, hemp, paper or other known tissue or filter paper.

U.S. Patent No. 5,090,975 issued to Requejo et al. Discloses a vacuum cleaner pouch comprising a sheet of fast spinning fibers without the need for a backing layer.

As a vacuum cleaning filter means, some of the desired characteristics of non-woven fabrics are that they must be air permeable but still have a high filtration efficiency. The air permeability is very important since the low permeability can result in a high pressure drop through the filter medium requiring a higher, and thus more expensive, energy input into the filtered fluid and shortening the filter life. The low permeability can also result in physical damage to the filter medium from being clogged with the filtered particles due to the increased pressure drop across the filter medium.

The high filtering efficiency is, of course, the main purpose for a filter medium and a high efficiency of the ability to maintain the efficiency at an acceptable level are key to the functioning of the filter media.

It is an object of this invention to provide a spunbonded polyolefin nonwoven fabric for use as a filter medium which has high permeability and high filtration efficiency. It is further an object of the invention to provide a filter means which is sufficiently rigid to be successfully converted into a finished filter. It is yet another object of this invention to provide a vacuum bag filter made from the filter medium wherein the filter media does not require a backing layer.

SYNTHESIS OF THE INVENTION The objects of this invention are achieved by a filter medium which is a non-woven fabric of conjugated spunbonded fibers. The fabric has a Frazie permeability of at least 250 cfm, an NaCl efficiency of at least 65%, a pressure drop of 0.5 or less mm H20, and a Gurley rigide of at least 20 mg. The tests mentioned here are described in the section "Test Methods". Conjugated fibers are made of polymers, more particularly d polyolefins, even more particularly of polypropylene and polyethylene in a side-by-side configuration. The filter medium is treated with a hot air knife and can be connected through air during the production processes. The medium is also treated with electret. The medium has a sufficient rigidity to convert to a filter or disk through conventional means such as by means of a cutting die. Even when the invention is mainly aimed at purifying the air filtrate, other gases can also be filtered.

BRIEF DESCRIPTION OF THE DRAWING The figure is a schematic drawing of a process line for making a filter medium of this invention.

DEFINITIONS As used herein, the term "non-woven fabric" refers to a fabric having a structure of individual fibers or yarns, which are interlocked, but not in an identifiable manner as in the woven fabric. Knitted fabrics have been formed from any processes such as, for example, meltblowing processes, bonding processes with spinning, and carded and bonded tissue processes. The basis weight of non-woven fabrics is usually expressed in ounce of material per square yard (osy) or grams per square meter (gsm) and useful fiber diameters are usually expressed in microns (note that to convert ounces per yard square to grams per square meter, multiply ounces per square yard by 33.91).

As used herein, the term "spun bonded fibers" refers to the small diameter fibers which are formed by extruding the melted thermoplastic material as filaments from a plurality of usually circular and fine capillaries into a spinning organ with the diameter of the extruded filaments, then being rapidly reduced, such as, for example, in U.S. Patent No. 4,340,563 issued to Appel et al., in Dorschner et al., U.S. Patent No. 3,692,618; in U.S. Patent No. 3,802,817 issued to Ma suky et al., in Kinney, U.S. Patent Nos. 3,338,992 and 3,341,344; in United States Patent No. 3,502,763 issued to Hartman, and United States Patent No. 3,5421,615 issued to Dob et al. Spunbonded fibers are generally sticky when they are deposited on the collector surface. Spunbonded fibers are generally continuous and have average diameters (from a sample of at least 10) greater than 7 microns, more particularly from around 10 and 20 microns.

As used herein, the term "co-melt blown fibers" means fibers formed by extruding a melted thermoplastic material through a plurality of capillary matrix vessels, usually circular and thin as melted filament yarns into a gas stream ( eg air), usually hot and high speed converging, which attenuate the filaments of melted thermoplastic material to reduce its diameter, which can be a microfibre diameter. Then, the meltblown fibers are carried by the gas stream at high speed and are deposited on a collecting surface to form a fabric of meltblown fibers disbursed at random. Such a process is described, for example, in United States Patent No. 3,849,241. The melt blown fibers are microfibers which can be continuous or discontinuous, are generally smaller than 10 microns in average diameter, and are generally sticky when deposited on a collecting surface.

As used herein the phrase "multiple-cap laminate" means a laminate wherein some of the layers are spun-bonded and some are formed by meltblowing such as a spin-bonded / melt-blown / spin-bonded laminate (SMS) and others as described in United States Patent No. 4,041,203 granted to Brock et al .; in U.S. Pat. No. 5,169,706 issued to Collier et al .; in U.S. Patent No. 5,145,727 issued to Potts et al .; in U.S. Patent No. 5,178,931 issued to Perkins et al. and in U.S. Patent No. 5,188,885 issued to Timmons et al. Such lamination can be done by depositing in a sequence on a mobile forming strip first a layer of spunbond fabric, then a melt-blown web layer and at the last another layer of spunbond material and then bonding the laminate to a web. com way is described below. Alternatively, the fabric layers can be made individually, collected in rolls, and combined in a separate bonding step. Such fabrics usually have a basis weight of from about 6 to 400 grams per square meter, more particularly from about 0.75 to about 3 ounces per square yard. The multiple layer laminates may also have multiple numbers of meltblown layers or multiple spun bonded layers in many different configurations and may include other materials such as the film materials (F) or coform materials, eg SMMS, SM, SFS , etc.

As used herein, the term "polymer" generally includes but is not limited to homopolymers, copolymers, such as, for example, block, d-graft, random and alternating copolymers, terpolymers, and the like, and mixing and modifications thereof. In addition, unless specifically limited otherwise, the term "polymer" will include all possible geometric configurations of the molecule. These configurations include, but are not limited to, isotactic, syndiotactic and random symmetries.

As used herein the term "machine direction" or MD means the length of a fabric in the direction in which it is produced. The term "machine transverse direction" or CD means the width of the fabric as, for example, an address generally perpendicular to the MD.

As used herein the term "conjugated fibers" refers to fibers which have been formed from at least two polymers usually extruded from separate extruders but spun together to form a fiber. Conjugated fibers are also sometimes referred to as multicomponent or bicomponent fibers. The polymers are usually different from each other even though the conjugated fibers can be monocomponent fibers. The polymers are arranged in distinct zones essentially constantly placed across the cross section of the conjugated fibers extending continuously along the length of the conjugated fibers. The configuration of such a conjugate fiber can be, for example, a pod / core arrangement where one polymer is surrounded by another or can be a side-by-side arrangement, or cake arrangement or an arrangement of "islands in the sea" . Conjugated fibers are shown in U.S. Patent No. 5,108,820 issued to Kaneko et al., In U.S. Patent No. 5,336,552 issued to Strack et al., And in U.S. Patent No. 5,382,400. awarded to Pike and others. For the two-component fibers, the polymers can be present in proportions of 75/25, 50/50, 25/75 or any other desired proportions.

As used herein, the term "biconstituent fibers" refers to fibers which have been formed from at least two extruded polymers from the same extruder as a mixture.The term "blend" is defined below. several polymer components arranged in different zones placed relatively constant across the cross-sectional area of the fibr the various polymers are usually non-continuous along the entire length of the fiber, instead of this it usually forms fibrils or protofibrils which start and end at random.

As used herein the term "compaction roller" means a set of rollers up and down the weave to compact the weave as a way to treat a newly produced microfiber, particularly a woven fabric spun in order to give it sufficient integrity for further processing, but not a relatively strong bonding of secondary bonding processes such as bonding through air, thermal bonding and ultrasonic bonding. The compaction rollers lightly squeeze the fabric in order to increase its self-adherence and therefore its integrity. The compaction rollers carry out this function well but have a number of disadvantages. One such disadvantage is that the compaction rollers actually compact the fabric, causing a decrease in the volume or elevation in the fabric which may be undesirable for the intended use. A second and more serious disadvantage of the compaction rollers is that the fabric is sometimes wrapped around one or both of the rollers, causing a closure of the fabric production line to clean the rollers, with the obvious loss companion in the production during the time of lack of work. A third disadvantage of the compaction rollers is that if a slight imperfection occurs in the formation of the fabric, such as a drop of polymer that is formed in the fabric, the compaction roller can force the drop into the band. perforated, on which s form most of the tissues, causing an imperfection in the band and ruining it.

As used herein, the term "hot air knife" or HAK means a pre-bonding or primary bonding process of a newly produced microfiber cloth, particularly spun-bonded to give it sufficient integrity, for example increasing the rigidity of the fabric for additional processing, but does not mean the relatively strong bonding of secondary bonding processes such as , thermal bonding and ultrasonic bonding. A hot air blade is a device which focuses a stream of heated air at a very high flow rate, generally from about 1000 to about 10000 feet per minute (fpm) (305 to 3050 meters per minute), or more particularly from about 3000 to 5000 feet per minute (915 to 1525 m / min) directed to the non-woven fabric immediately after its formation. The air temperature is usually in the range of the melting point of at least one of the polymers used in the fabric, generally between about 200 and 550 ° F (93 and 290 ° C) for the thermoplastic polymers commonly used in the fabric. the union co yarn. Control of air temperature, speed, pressure, volume and other factors helps to avoid tissue damage while integrity is increased. The focused air stream of the hot air blade is arranged and directed by at least one slot of about 3 to 25 millimeters in width, particularly of about 9.4 millimeters, which serves as the outlet for the heated air to the fabric , with the groove running in a direction essentially transverse to the machine over substantially the full width of the fabric. In other embodiments, there may be a plurality of grooves arranged close together or separated by a slight gap. The at least one groove is usually continuous, even if not essentially continuous and may be composed of for example closely spaced holes. The hot air blade has a plenum to distribute containing the heated air before its exit from the slot. The plenum pressure of the hot air blade is usually between about 2 to 22 mmHg of water and the hot air blade is positioned between about 0.25 and 10 inches more preferably between 0.75 to 3.0 inches (19 to 76 mm) ) above the forming wire. In a particular embodiment the cross-sectional area of the plenum of the hot air knife for the flow in the transverse direction (for example the cross-sectional area of the plenum in the machine direction) is at least twice the area of Total slot output. Since the perforated wire upon which the spin-bonded polymer is formed generally moves at a high speed rate, the exposure time of any particular part of the fabric to the air discharged from the hot air blade is less than one tenth of a second and generally about one hundred thousandth of a second in contrast to the process of bonding through air which has a much longer residence time. The hot air knife process has a greater range of variability and control of many factors such as air temperature, speed, pressure, volume, slot or orifice arrangement and the size and distance from the full of the hot air knife to the fabric. The hot air blade is further described in United States Patent Application No. 08 / 362,328 to Arnold et al., Filed December 22, 1994 and commonly assigned.

As used herein, "ultrasonic bonding" means a process carried out, for example, by passing the fabric between a sonic horn and an anvil roll as illustrated in U.S. Patent No. 4,374,888 issued to Bornslaeger. .

As used herein, "thermal point bonding" involves passing a woven fiber that is to be joined between a heated calender roll and an anvil roll. The calendering roll is usually, though not always, patterned in some manner so that the entire fabric does not bond across its entire surface, and the anvil roller is usually flat. Typically, the percent bond area varies from about 10% to about 30% of the area of the woven laminate fabric. As is well known in the art, the knit joint holds the laminate layers together as well as imparts integrity to each individual layer by joining the filaments and / or fibers within each layer.

As used here, the binding through air or " " means a joining process of a non-woven bicomponent fiber fabric in which the air which is hot enough to melt one of the polymers from which the fibers of the fabric are made is forced through the fabric. The air speed is between 100 and 500 feet per minute and the dwell time can be as long as 6 seconds. The melting and resolidification of the polymer provides the bond. The union through air has a relatively restricted variability and since the union through air requires the melting of at least one component to achieve the union, this is restricted to tissues with two components such as conjugated fibers or those which include an adhesive. At the junction through air, the air having a temperature above the melting temperature of one component and below the melting temperature of another component is directed from a surrounding cover, through the fabric and up to a perforated roller holding the tissue. Alternatively, the air-binding device can be a flat arrangement in which the air is directed vertically downwards on the fabric. The operating conditions of the two configurations are similar, the primary difference being the geometry of the fabric during joining. The hot air melts the lower melt polymer component and thus forms the bonds between the filaments to integrate the fabric.

TEST METHODS Frazier Permeability: A measurement of the permeability of a fabric to the air is the Frazier permeability which is carried out according to the Federal test standard No. 191A, method 5450 dated July 20, 1978 and reported as an average of three sample readings. The Frazier permeability measures the rate of air flow through the tissue in cubic feet of air per square foot of tissue per minute or cfm. Convert cfm to liters per square meter per minute (LSM) by multiplying CFM by 304.8.

NaCl Efficiency: The NaCl efficiency is a measure of the ability of a fabric to stop the passage of small particles through it. A higher efficiency is generally more desirable and indicates a greater ability to remove particles. An NaCl efficiency is measured in percent according to the TSI Inc. Model 8110 Automated Filter Tester Operation Manual, February 1993, P / 1980053, revision D, at a flow rate of 32 liters per minute using particles from NaCl of 0.1 micron size and is reported as an average of at least 3 sample readings. The manual is available from TSI Inc., at P.O. Box 64394, 500 Cardigan Road, St. Paul, Minnesota 55164.

Pressure drop: The pressure drop is a measure during the NaCl efficiency test by taking the static pressure readings up and down the fabric and calculate the pressure drop as Pl-P2 = dP where Pl is the pressure upwards, P2 is the downward pressure and dP is the difference in pressure or fall through the tissue. The results are reported in millimeters of water (mm H20).

Melt flow rate: The melt flow rate (MFR) is a measure of the viscosity of a polymer. The melt flow rate is expressed as the weight of material flowing from a capillary vessel of known dimensions under a specified load or a cutoff rate for a measured period of time and is measured in grams / 10 minutes at a temperature already set a load according to, for example the test AST 1238-90b.

Gurley stiffness: The Gurley stiffness test mid bending resistance of a material. It is carried out according to the method TAPPI T 543 om-94 is measured in milligrams and reports on an average of five sample readings. The sample size used for the test here was 3.8 centimeters in the machine direction by 2.54 centimeters in the direction transverse to the machine.

DETAILED DESCRIPTION The fabric of filter media of this invention is made by a spinning bonding process. The spinning process generally employs a hopper which supplies the polymer to a heated extruder. The extruder supplies the heated polymer to a spinning organ wherein the polymer is fiberized as it passes through the fine openings arranged in one or more rows of a spinning organ, forming a curtain of filaments. The filaments are usually cooled with air at a low pressure, pulled, usually pneumatically and deposited on a mobile foraminous ester, band or "forming wire" to form the non-woven fabric. The polymers useful in the co-bound processes generally have a melting temperature of between about 200 ° C to 320 ° C.

The fibers produced in the spunbonded process are usually in the range of from about 10 about 50 microns in average diameter, depending on the process conditions and the desired end use for the fabrics to be produced from such fibers. . For example, increasing the molecular weight of the polymer or decreasing the processing temperature results in larger diameter fibers. Changes in the temperature of the cooling fluid and in the pneumatic pulling pressure can also affect the fiber diameter. The fibers used in the practice of this invention usually have average diameters in the range of from about 7 to about 35 microns, more particularly from about 15 to about 25 microns. Furthermore, when reference is made to "average" diameters, it is meant that this is an average of at least 10 samples.

The areas in which the tissue of this invention can find utility are in the filtrate. More particularly, the fabrics produced according to this invention are useful in heavier weight basis applications such as in vacuum cleaner discs or bags and in lighter basis weights such as vacuum bag liners. The filter media fabrics can have basis weights ranging from about 17 grams per square meter to about 340 grams per square meter or more particularly from about 51 grams per square meter to about 170 grams per square meter, yet more particularly around 68 grams per square meter.

The fibers used to produce the fabric of this invention are conjugated fibers such as fibers side by side (S / S). The polymers used to produce the fibers can be polyolefins, particularly polypropylene and polyethylene. When the conjugate fibers are produced and cooled, the coefficients that differ from the expansion of the polymers cause these fibers to bend and finally curl, somewhat due to the action of the bimetallic strip in a conventional room thermostat. Generally, by increasing the curl of the fibers, the volume of the tissue increases, the permeability of the fabric or fabric increases, and the rigidity of the fabric decreases. Fibers which vary in crimping from a high crimp to very low crimp may be used in the practice of this invention depending on the stiffness and the permeability requirements of the user.

Many polyolefins are available for the production of fiber, for example polyethylene such as ® Dow Chemical ASPUN 68A linear low density polyethylene, LLDPE 2553 and 25355 and 12350 high density polyethylene such as suitable polymers. The polyethylenes have melt flow rates in g / 10 min at 190 ° F and a load of 2.16 kilograms of around 26, 40, 25 and 12 respectively. Polypropylenes that form fibers include polypropylene ® ESCORENE PD 3445 from Exxon Chemical Company and PF-304 from Himont Chemical Company. Many other polyolefins are commercially available.

After the fibers are curled and deposited on the forming wire and create the fabric of this invention, the fabric can be passed through an air knife or HAK to very lightly consolidate it and provide sufficient integrity for further processing.

After depositing but before the hot air knife treatment, the crimped fiber fabric has a low stiffness which makes it difficult, if impossible, to successfully convert over commercially available conversion equipment commonly used for the manufacture of discs and vacuum bags. One aspect of this invention provides a means for using a nonwoven fabric having crimped fibers while also providing sufficient stiffness to manufacture the vacuum bags and discs as by applying the hot air knife to the fabric. The application of the hot air fabric allows the formation of a fabric of crimped fibers to deliver high permeability and rigidity by melting only a portion of the lower melt component in the fabric, preferably only the lower melting component on the side facing the hot air blade in the primary union or pre-union step. This hot air blade step creates an area of pre-assembled crimped fibers located on one side of the fabric which then undergoes a second melt when exposed to the joint via air. The exposure of this zone to at least two cycles of melting and heating is believed to create a zone of high rigidity in the weave of polymer crystallization, however, since this zone is composed of a small percentage of the total tissue , the effect on tissue permeability is minimized. This differs from the commonly used method of increasing the integrity of the fabric known as compaction rollers since, while the compaction rollers increase the stiffness of a fabric, they also reduce the permeability of said fabric. Note that when the compaction rollers can be used in the practice of this invention, the hot air knife is essentially preferred.

After treatment with the hot air knife, the fabric is sufficiently cohesive to move it to the next production step; the secondary union step. The secondary bonding process which can be used in the practice of this invention is an air binding because it does not appreciably reduce the pore size of the weave and therefore the permeability. When used with the hot air knife pre-junction, air binding effectively produces high stiffness in the fabric since it provides a second heating of the polymer previously heated by the hot air knife and provides a sufficient heat to the bonded fibers not joined by the hot air knife. This creates joints at almost every fiber crossing point, thereby restricting the movement of most of the fibers in the fabric. The union of thermal point in contrast results in joints in discrete points, thus allowing the fibers between the joining points the freedom to bend and rotate individually and thus produce a much smaller increase in rigidity and thus is not a process of bond acceptable for this invention.

Another method to increase the rigidity of the fabric is by simply increasing the base weight of the fabric. This technique, however, is undesirable, since this also increased the cost of the non-woven fabric. This is undesirable because the overall permeability of the fabric is reduced again. The hot air blade in conjunction with the air binding allows the increase of a fabric stiffness without the cost penalty associated with increasing the base weight of the fabric and without adversely affecting the permeability of the nonwoven fabric.

After bonding through air, the fabric is treated with electret. The treatment with electret also increases the efficiency of filtering by pulling the particles that are going to be filtered to the filter by virtue of the electric charge. The treatment with electret can be carried out with a number of different techniques. One technique is described in U.S. Patent No. 5,401,446 issued to Tsai et al. And assigned to the Tennessee Research Corporation University and incorporated herein by reference in its entirety. Tsai describes a process by which a fabric or film is subsequently subjected to a series of electric fields so that the adjacent electric fields have polarities essentially opposite each other. Therefore, one side of the fabric or film is initially subjected to a positive charge while the other side of fabric or film is initially subjected to a negative charge. Then, the first side of the fabric or film is subjected to a negative charge and the other side of the fabric or film is subjected to a positive charge. Such fabrics are produced with a relatively high charge density without a static electric charge of inherent surface. The process can be carried out by passing the fabric through a plurality of electric fields that do not form scattered arcs which can be varied over a range depending on the desired load in the fabric or fabric. The fabric can be charged to a range of about 1 kVDC / cm to 12 kVDC / cm or more particularly 4 kVDC / cm to 10 kVDC / cm and even more particularly 7 kVDC / cm to about 8 kVDC / cm.

Other methods of treatment with electret are known in the art as described in the patents of the United States of North America Nos. 4,215,682 granted to Kubik others, 4,375,718 granted to Wadsworth, 4,592,815 granted to Nakao and 4,874,659 granted to Ando.

Returning to the figure, a process line 10 for preparing an embodiment of the present invention is described. The process line 10 is arranged to produce conjugated continuous filaments, but it should be understood that the present invention comprises non-woven fabrics made with multi-component filaments having more than two components. For example, the fabric of the present invention can be made co filaments having three or four components. The process line 10 includes a pair of extruders 12a and 12b for separately extruding a polymer component A and a polymer component B. The polymer component A is fed into the respective extruder 12a from a first hopper 14a and the polymer component B is fed into the respective extruder 12b from a second hopper 14b. The polymer components A and B are fed from the extruders 12a and 12b through the respective polymer conduits 16a and 16b to a spinner member 18. The spinners for extruding the conjugated filaments are well known to those of ordinary skill in the art. art and therefore are not described in detail here. Generally described, the spinner member 18 includes a box containing a spin pack which includes a plurality of plates stacked one on top of the other with a pattern of apertures arranged to create flow paths to direct polymer components A and B separately to through the spinner organ. The spinner member 18 has the openings arranged in one or more rows. The openings of the spinning member form a curtain of filaments that extends downwardly when the polymer is extruded through the spinning organ. For the purposes of the present invention, the spinner member 18 may be arranged to form eccentric sheath / core conjugate filaments or side by side, for example.

The process line 18 also includes a cooling blower 20 positioned on one side of the filament curtain extending from the spinner member 18. The air of the cooling air blower 20 cools the filaments extending from the spinner member 18. The cooling air can be directed from one side of the filament curtain as shown in Figure 1, or from both sides of the filament curtain.

A vacuum cleaner or fiber pulling unit 22 is placed below the spinner member 18 and receives the cooled filaments. Fiber pulling units or vacuum cleaners for use in melt spinning polymers are well known as discussed above. Fiber pulling units suitable for use in the process of the present invention include a linear fiber vacuum cleaner of the type shown in US Pat. Nos. 3,802,817 4,340,563 and eductive guns of the type shown in the patents of US Pat. United States of North America Nos. 3,692,618 3,423,266.

Generally described, the fiber pull unit 22 includes an elongated vertical conduit through which the filaments are pulled by sucking the air that enters from the sides of the conduit and flows down through the conduit. A heater 24 supplies the hot suction air to the fiber pulling unit 22. The hot suction air pulls the filaments and the ambient air through the fiber pulling unit.

An endless foraminous forming surface 26 is placed below the fiber pulling unit 22 and receives the continuous filaments from the outlet opening of the fiber pulling unit. The forming surface 26 travels around the guide rollers 28. A vacuum 30 placed below the forming surface 26 where the filaments are deposited pulls the filaments against the forming surface.

The process line 10 as shown also includes a hot air blade 34 which provides a degree of integrity to the fabric. In addition, the process line includes a joining apparatus which is an air-through linker 36. After passing through the linker through air, the fabric is passed between a loading bar or wire 48 and a loaded roller 42. and then between a second wire or loading bar 50 and a roller 44.

Finally, the process line 10 includes a rolling roller 42 to take the finished fabric.

To create the process line 10, the hoppers 14a and 14b are filled with the respective polymer components and B. The polymer components A and B are melted extruded by the respective extruders 12a and 12b through the polymer conduits 16a and 16b and the spinner organ 18.

Although the temperatures of the melted polymers may vary depending on the polymers used when polypropylene and polyethylene are used as components A and B respectively, the preferred temperatures of the polymers range from about 370 ° to about 530 ° F. , preferably ranging from about 400 to about 450 ° F.

As the extruded filaments extend below the spinner member 18, a stream of air from the cooling blower 20 at least partially cools the filaments to develop a latent helical ripple on the filaments at a temperature of about 45 ° to about 90 °. , and at a speed of from 100 to about 400 feet per minute. Alternatively, the cooler can be used to minimize curling if desired.

After cooling, the filaments are pulled into the vertical duct of the fiber pulling unit 22 by means of the flow of hot air from the heated one. 24 through the fiber pull unit. The fiber javel unit is preferably positioned 30 to 60 inches below the bottom of the spinner member 18. The temperature of the air supplied from the heater 24 is sufficient to, after some cooling due to mixing with the cooler ambient air, sucked with the filaments, the air heats the filaments to a temperature required to activate the latent ripple. The temperature required to activate the latent curling of the filaments varies from about 110 ° F to a maximum temperature lower than that of the melting point of the melting component lower which for the materials of bonding through air is the second component B. The temperature of the air from the heater 24 and thus the temperature at which the filaments are heated can be varied to achieve different crimping levels. Generally, a higher air temperature produces a higher ripple number. The ability to control the degree of curling of the filaments is a particularly advantageous feature of the present invention because it allows one to change the resulting density, pore size distribution and tissue drop by simply adjusting the temperature of the fabric. air in the fiber pull unit.

The crimped filaments are deposited through the outlet opening of the fiber pulling unit 22 on the moving forming surface 26. The vacuum 20 pulls the filaments against the forming surface 26 to form a non-woven fabric not united of continuous filaments. The tel is then given a degree of integrity by the hot air blade 34 and is attached through air in the linker through air 36.

In the air-binding unit 36, the air has a temperature above the melting temperature of the component B and below the melting temperature of the component A it is directed from the cover 40, through the fabric and up to the perforated roller 38 Alternatively, the air through linker may be a flat arrangement where the air is directed vertically downward over the tissue. The conditions on the two configurations are similar, the primary difference being the geometry of the tissue during the union. The hot air melts the lower melted polymer component B and forms the bonds between the conjugate filaments to integrate the fabric. When polypropylene and polyethylene are used as components of polymer A and respectively, the air flow through the junction through d air usually has a temperature ranging from about 110 ° C to 162 ° C and a speed of from about from 100 to 500 feet per minute. It should be understood, however, that the parameters of the binding agent through air depend on factors such as the type of polymers used and the thickness of the fabric.

The weave is then passed through the charged field between the loading wire or bar 48 and the loading drum 42 and then through a second charged field of opposite polarity created between the loading bar or wire 50 and the drum or loading roller 44. The fabric can be loaded in the range of about 1 kVDC / cm to 12 kVDC / cm.

Finally, the finished fabric is wound onto the winding roll 42 and is ready for further processing or use.

The three key attributes for the desired filter medium of this invention are the Frazier permeability (P), the NaCl efficiency (E), and the Gurley stiffness (S) and the pressure drop. Note that in the calculation of S, the stiffness is normalized to the basis weight by dividing the Gurley stiffness in milligrams by the basis weight in grams per square meter (mg / gsm). It is believed that the filter medium produced according to this invention must have a Frazier permeability of more than about 250 CFM, an NaCl efficiency of more than about 65%, a pressure drop of 0.5 or less mm H20, a stiffness Gurley of at least around 20 mg.

The filter medium of this invention can be made in a vacuum bag filter or filter by any suitable means known in the art. Vacuum disc manufacturing generally involves the step of cutting the fabric by a die cut. The discs produced from the fabric of this invention are stiffer than, for example, meltblown fabrics, and thus problems such as edge bonding when cutting more than one layer at a time are avoided. In addition to a more "clean" or sharp cut, the fabric of this invention is also less weak than co-melt blown fabrics and thus is also easier to handle. The fabric can be converted into a vacuum bag by cutting, bending and joining (eg gluing) either alone or with a laminate.

The following sample data numbered 1-7 includes the comparative examples (6 and 7), and examples of the fabrics of the invention (1-5) and show the characteristics of the fabrics which satisfy the requirements of this invention against of those who do not.

The fabrics of this invention comprise fiber bonded by side-by-side conjugate yarns made in accordance with US Pat. No. 5,382,400 issued to Pike et al. The polymers used were ESRO® polypropylene ESCORENE PD-3445 and ASPUN 6811A linear low density polyethylene available from Exxon Chemical Company of Houston, Texas, and Dow Chemical Company of Midland, respectively.

Michigan. In samples 1-5, the air flow rate of the hot air blade was between about 5000 to 6000 feet per minute (1524-1830 m / min). The temperature of the hot air knife was 163 ° C and the height of the hot air knife above the fabric was 2.5 centimeters. Samples 1-5 were extruded through spinning organs having a diameter of 0.6 millimeters to produce fibers having diameters of from 18 to 22 microns. Samples 1-5 used ® ® polypropylene ESCORENE PD-3445 from Exxon and ASPUN polyethylene 6811 from Dow and processed at a melting temperature of about 232 ° C. Samples 1-5 were processed through a linker through air at a temperature of between about 91-134 ° C at an air rate of between 107-198 m / min for a period of time of about 3 to 5 seconds. Samples 1-5 were treated according to the method of U.S. Patent No. 5,401,446 by passing the tissue between a wire or conductive bar and a curved conductive drum with an electric field that does not form an arc between the bar or wire and the drum of about 7 kVDC / cm of separation between the bar and the drum and then pass the weave through a second electric field generated by the same means and as the same force as the first but with the orientation of field being 180 ° of the first in relation to the woven.

"The comparative fabrics of samples 6 and 7 are from DieCut Products, Company, of Cleveland, Ohio, and are fabrics or fabrics commonly used in vacuum cleaner discs .. Fabric 6 is a blown fabric with polyester fusing and fabric 7 is blowing fabric with olefin fusion It is not known whether it was treated with electret.

After training, the fabrics were tested for permeability, stiffness, pressure drop and efficiency according to the methods given here and the results are shown in Table 1.

TABLE 1 The results show that the filter medium of this invention, samples 1-5 has a good combination of permeability, efficiency, pressure drop and stiffness. This is most notable when comparing, for example, the sample 7 which, even though it provides a very good efficiency, is very low in permeability and inversely very high in pressure drop.

Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications to example embodiments are possible without departing materially from the teachings and novel advantages of this invention. Therefore, all modifications are intended to be included within the scope of the invention as defined in the following claims. In the claims the media clauses plus function is intended to cover the structures described herein as carrying out the recited function and not only the structural equivalents but also the equivalent structures. Thus even when a nail and a screw may not be structural equivalents in the sense that a nail employs a cylindrical surface to secure wooden parts together, while a screw employs a helical surface, in the environment of the wooden parts of Clamping, a nail and a screw can be equivalent structures.

It should also be noted that any parts, applications or publications mentioned herein are incorporated by reference in their entirety.

Claims (8)

R E I V I N D I C A C I O N S

1. A filter for vacuum cleaners comprising a nonwoven fabric of conjugate fibers bonded with yarn having a Frazier permeability of at least 250 CFM, an NaCl efficiency of at least 65 percent, a pressure drop of 0.5 or less mm H20 and a Gurley stiffness of at least 20 mg, wherein said fabric has been subjected to a hot air knife treatment.

2. The filter, as claimed in clause 1, characterized in that it has a basis weight of around 51 grams per square meter and about 170 grams per square meter.

3. The filter, as claimed in clause 1, characterized in that said fibers are composed of polypropylene and polyethylene in a side-by-side configuration.

4. The filter, as claimed in clause 3, characterized in that it is formed by a process e where the fabric is subjected to a bond through air.

5. The filter, as claimed in clause 4, characterized in that it is formed by a process in which said fabrics are subjected to an electret treatment.

6. A vacuum bag comprising the filter medium as claimed in clause 1.

7. A filter for vacuum cleaner comprising a non-woven fabric of conjugated fibers joined by spinning on the side of polypropylene / polyethylene curled having a basis weight of between about 51 grams per square meter and about 170 grams per square meter and having a Frazier permeability of at least 250 CFM, an NaCl efficiency of at least 65 percent, a pressure drop of 0.5 or less mm H2 and a Gurley stiffness of at least 20 mg, formed by a process in the that said fabric is subjected to a treatment of hot air knife, bonding through air and treatment of electret.

8. The filter for vacuum cleaner, as claimed in clause 7, which is cut with a matrix. SUMMARY A filter medium for vacuum cleaner is provided which is a fabric bonded by non-woven yarn of conjugated spunbonded fibers. The fabric has a frazie permeability of at least 250 CFM, an NaCl efficiency of at least 65 percent, and a Gurley stiffness of at least 20 mg, and a pressure drop of 0.5 or less mm H20. The conjugated fibers are made of polymers, more particularly of polyolefins, even more particularly of polypropylene and polyethylene in a side-by-side configuration. The filter medium is treated with a hot air knife and is bonded through air during the production process. The medi is also treated with electret. The medium has sufficient stiffness to become a filter through conventional means. While this invention is directed primarily to the purification and filtering of air, other gases can also be filtered.