MXPA97002931A - High densi non-woven filter medium - Google Patents

Abstract

The invention provides a sheet filter means having autogenously bonded non-crimped conjugated fibers which contains a polyolefin and another thermoplastic polymer having different melting points. The filter medium has a density between about 0.07 g / cm3 and about 0.2 g / cm3. The invention further provides a three-dimensionally thermoformed filter medium having a density of between about 0.07 g / cm3 and about 0.5 g / c.

Description

HIGH DENSITY NON-WOVEN FILTER MEDIUM BACKGROUND OF THE INVENTION The present invention relates to a non-woven fabric produced from conjugated fibers. More specifically, the invention relates to a filter media of a non-woven fabric of conjugated fiber.

Porous nonwoven sheet media, such as compounds containing microfiber fabrics sprayed with solution or formed by meltblowing and conventional spin-bonded fabrics have been used in various filtering applications, for example filtering cooler, cutting fluid filtration, pool filtering, transmission fluid filtering, air filtering of rooms and automotive air filtering. In liquid filtering applications, especially for large volume filtration applications, for example, cutting fluid filtration and coolant, the contaminated liquid is typically driven by pressure on horizontally placed filter media. Consequently, the filter medium requires being strong enough to withstand the weight of the liquid and the applied pressure of the flow. As such, the liquid filter medium needs to provide high strength properties in addition to the proper levels of filter efficiency, capacity and durability.

In general, the composite filter media is formed by laminating a layer of a microfiber fabric over a highly porous support layer or between two highly porous support layers since the microfiber layer does not have sufficient physical strength to be self-supporting . Consequently, the production process for a composite filter medium requires not only different layer materials but also requires the formation of an elaborate layer and lamination steps, making the filter medium very costly. Even when the self-supporting single-layer microfiber filter media can be produced in order to avoid the complexity of the formation of composite filter media by increasing the thickness of the microfiber filter layer, the pressure drop through such Thick microfiber filter media is unacceptably high, making the microfiber medium unsuitable for filtering applications, especially for high production filtration applications. A further disadvantage of existing microfiber filter media and laminated filter media containing microfiber fabrics is that they tend to exhibit weak physical properties. Consequently, these filter media are not particularly useful for large volume liquid filtering applications.

Other sheet filter media widely used in the industry are cellulose fiber fabrics of pulp fibers thermomechanically or chemically processed. Cellulosic fiber media are, for example, commonly used in automobile fuel and oil filters and in vacuum cleaner filters. However, cellulosic fiber filter media tend to have limited filtering efficiency and do not provide the high strength properties that are required for high volume and high pressure liquid filtering applications.

Still another group of filter media that has been used in liquid filtration applications are non-woven fabrics bonded by spinning and calendering, especially fabrics bonded by polyester spinning. For example, calendered polyester spunbonded filter media is commercially available from Reemay, Inc., under the trademark Reemay. Typically, the yarn-bonded filter media is formed from the melt spinning of a physical mixture of structural filaments and binder filaments, randomly and isotropically depositing the filaments on a forming surface to constitute a non-woven fabric, and then calendering the non-woven fabric to activate the binding filaments to effect the adhesive bonds, forming a sheet filter means having a relatively uniform thickness. These calendered sheet filter media exhibit good strength properties. However, the efficiency of the filter of these filter media joined by spinning is, in general, significantly lower than that of the microfiber filter media. In addition, the porosity distribution on the surface of the filter media joined by spinning and calendering tends to be non-uniform. This is because when the spun filaments are randomly deposited on the forming surface, the density of the filament, for example, the number of strands of filament deposited for a given area of surface, or the deposited tissue varies from one section to another; and when the deposited fiber fabric is calendered and compacted to a uniform thickness, the high fiber density and low fiber density sections form the low porosity and high porosity sections, respectively. Consequently, filter media joined by spinning and calendering tend to have a non-uniform porosity distribution.

There is still a need for inexpensive filter media that provides a highly desirable combination of high filtering efficiency and capacity and high physical strength.

SYNTHESIS OF THE INVENTION The invention provides a sheet filter means having autogenously bonded non-crimped conjugate fibers. The filter medium has a density of between about 0.07 g / cm3 and about 0.2 g / cm3 and a Frazier permeability of at least 3.5 m3 / min / m2, and the conjugate fibers have a polyolefin and a thermoplastic polymer having a melting point higher than that of the polyolefin. The medium has a Mullen breaking strength of at least 3.5 kg / cm2, and the medium is particularly suitable for filtering liquids.

The invention also provides a thermoformed three-dimensional filter medium having autogenously bonded non-crimped conjugated fibers selected from spunbonded fibers and short fibers containing a polyolefin and another thermoplastic polymer, wherein the polyolefin and the thermoplastic polymer have melting curves of analysis Different differential calorimetry so that an exposure to a temperature that melts about 50% of the lowest melted polyolefin component melts equal to or less than about 10% of the other thermoplastic component. The thermoformed filter medium has a density between about 0.07 g / cm3 and about 0.5 g / cm3.

The conjugated fibers as used herein indicate fibers having at least two different component polymer compositions which occupy different cross sections along essentially the entire length of the fibers. The term "fibers" as used herein indicates both discontinuous fibers and continuous filaments, for example, short fibers. The term "spunbond fibers" refers to the fibers formed by extruding the melted thermoplastic polymers as continuous filaments from a plurality of spinnaker capillaries, usually circular and relatively thin, and then quickly pulling the extruded filaments through the fibers. of an eductive pulling mechanism or another known to impart a molecular orientation and a physical resistance to the filaments. The continuously drawn filaments are deposited on a foraminous forming surface in a highly random manner to form a non-woven fabric having essentially a uniform density. A vacuum apparatus can be placed below the forming surface around the region where the fibers are deposited to facilitate proper placement and distribution of the fibers. Then, the deposited non-woven fabric is bonded to impart physical integrity and strength. The processes for producing the spunbonded fibers and the fabrics thereof are discussed, for example, in U.S. Patent Nos. 4,340,563 issued to Appel et al .; 3,692,618 issued to Dorschner and others and US Pat. No. 3,802,817 issued to Matsuki et al. In accordance with the present invention, the filter medium desirably contains continuous conjugated filaments, for example, conjugated fibers spun-bonded, since the continuous filaments provide improved strength properties and do not tend to produce lint. The term "not curled" as used herein indicates that the fibers have not been subjected to texturing or fiber curling processes and desirably have less than two crimps per extended inch as measured in accordance with AST D-3937- 82 The term "uniform fiber coverage" as used herein indicates an essentially uniform or uniform fiber coverage achieved by the processes of depositing random or isotropic fibers or filaments.

The nonwoven filter media of the present invention are highly suitable for various filter applications that require high filter efficiency, high physical strength, high abrasion resistance, thermoformability and the like. Additionally, the non-woven filter medium is highly suitable for converting it into a high-fold density filter medium.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 are DSC melt curves for polyethylene and linear low density polypropylene.

Figure 2 are DSC melt curves for linear low density polyethylene and nylon 6.

Figure 3 illustrates an air-through union which is suitable for the present invention.

Figure 4 illustrates a suitable folding process.

Figure 5 is a graph of the filter efficiencies of various filter media with respect to their densities.

Figure 6 is a graph of the filter lives of various filter media with respect to their densities.

Figure 7 is a graph of the initial filter efficiencies of various filter media with respect to their densities.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a nonwoven or non-crimped conjugate fiber nonwoven filter media. The filter medium is highly useful for filtering liquids. The filter medium has a density between about 0.07 g / cm3 and about 0.2 g / cm3, desirably between about 0.08 g / cm3 and about 0.19 g / cm3, more desirably between about 0.1 g / cm3 and about 0.15 g / cm3 and a permeability of at least about 15 m3 / min / m2, desirably between about 15 m3 / min / m2 and about 90 m3 / min / m2, more desirably between about 18 m3 / min / m2 and about 76 m3 / min / m2, more desirably between about 300 m3 / min / m2 and about 60 m3 / min / m2, as measured according to the Federal test method 5440, Standard No. 191A. The conjugate fiber nonwoven filter medium is characterized by having a desirable combination of useful filter attributes including a high density, a high strength, a smooth surface and a relatively uniform porosity distribution. The desirable characteristics of the present filter means are attributable to the single approach to produce the nonwoven sheet media. The filter medium of the present invention is air-dried, and is not calendered, but the filter medium can still be produced to have a high density and a low rise that are comparable to those of the non-filter media. calendered fabrics.

The conjugated fibers contain at least two polymer components that have had different melting points, a higher melting polymer and a lower melting polymer, and the lower melting polymer occupies at least about 25%, desirably so minus 40%, more desirably at least about 50% of the total peripheral surface along the length of the fibers such that the lower melt polymer can be heat activated to become adhesive and form interfiber bonds autogenous, while the higher melted polymer retains the structural integrity of the fibers. The present filter media containing the conjugate fibers forming the autogenous interfiber bonds exhibits high strength properties, especially multidirectional resistance. Such multidirectional resistance can be measured with the ASTM D3786-87 test, from the Mullen Burst test. The filter medium has a Mullen Burst strength of at least 3.5 kg / cm2, desirably at least 4 kg / cm2, more desirably at least 4.5 kg / cm2.

Although the conjugated fibers present may contain more than two component polymers, the present invention hereinafter shown with conjugated fibers having two polymer components (bicomponent fibers). The component polymers are selected from the fiber-forming thermoplastic polymers and the polymers have a melting point difference of at least about 5 ° C, desirably at least about 10 ° C. Since thermoplastic polymers generally do not melt at a specific temperature, but instead melt over a temperature dimension, the melt temperature difference between the lower melt polymer component and the higher melt component polymer can best be defined by melt curve measurements in a conventional differential analysis calorimetry (DSC) apparatus. Even if two polymers could have significantly different melting points, which are generally defined as the peak of the melting DSC curve, the polymers can melt simultaneously over a temperature range due to the overlap of melting curve temperature ranges. In accordance with the present invention, the component polymers are selected such that at a temperature at which 50% of the lower melt polymer is melted, as defined by the DSC melt curve of the polymer, more melt the polymer equal to or less than 10%, desirably equal to or less than 5%. More desirably, the DSC melt curves of the component polymers do not overlap at all. And more desirably, the melt DSC curves of the component polymers are separated by at least some degrees. The component polymers selected according to the melting point selection criteria of the present invention provide a beneficial combination of thermal and physical properties so that the lower melt component polymer can be thermally adhesive while the other polymers of The components maintain the physical integrity of the fibers, thus forming the strong interfiber bonds without sacrificing the physical integrity of the non-woven fabric or requiring a compaction pressure. In addition, when the DSC melt curves do not overlap, the difference between the melting temperature ranges allows the non-woven fabric to be still heated to a temperature at which the lower melt component polymer melts and allows the flow and spreading within the fiber structure without losing the structural integrity of the fabric. The flow of the lower melt polymer, in general, improves the abrasion resistance and strength and increases the density of the fabric, producing a more compact filter medium. For example, polyethylene and linear low density polypropylene are highly suitable component polymers for conjugate fibers since the DSC melting curves of the polymers do not overlap at all, as shown in Figure 1. The first embedded in the The melting curve of Figure 1 is the melt curve of the linear low density polyethylene and the second embedded curve is the melting curve of the polypropylene. Figure 2 is another example of a polymer combination suitable for conjugate fibers. The DSC melt curves, as shown in Figure 2 for linear low density polyethylene and nylon 6 are significantly separated. The first significant embedment in the melting curve of Figure 2 is the melting curve of linear low density polyethylene and the second embedded is the melting curve of nylon 6. The melting curves show that melting temperature ranges of the two polymers are significantly different, making the polymers highly suitable for the present invention.

In accordance with the present invention, the lower melt component polymer is selected from polyolefins, and the lower melt polymer constitutes between about 10% by weight and about 90% by weight, desirably between about 30% by weight and 80% by weight, more desirably between about 40% by weight and about 70% by weight of the fibers based on the total weight of the fibers. The polyolefin is selected from polyethylene, for example, linear low density polyethylene, high density polyethylene, low density polyethylene and medium density polyethylene; polypropylene for example, isotactic polypropylene, syndiotactic polypropylene, mixtures thereof and mixtures of isotactic polypropylene and atactic polypropylene; polybutylene, for example, poly (1-butene) and poly (2-butene); and polypentene, for example, poly-4-methylpentene-1 and poly (2-pentene); as well as the mixtures and copolymers thereof, for example the ethylene-propylene copolymer, the ethylene-butylene copolymer and the like.

The other component polymers for the conjugated fibers are selected from polyolefins, polyamides, polyesters, polycarbonates and mixtures and copolymers thereof, as well as copolymers containing acrylic monomers, provided that the other component polymers are selected in accordance with the criteria of melting point selection described above. Suitable polyolefins include polyethylene, for example, linear low density polyethylene, high density polyethylene, low density polyethylene and medium density polyethylene; polypropylene, for example, isotactic polypropylene, syndiotactic polypropylene, mixtures thereof and mixtures of isotactic polypropylene and atactic polypropylene; polybutylene, for example, polydimethane) and poly (2-butene); and polypentene, for example, poly-4-methylpentene-1 and poly (2-pentene); thus the mixtures and copolymers thereof. Suitable polyamides include nylon 6, nylon 6/6, nylon 10, nylon 4/6, nylon 10/10, nylon 12, nylon 6/12, nylon 12/12, and hydrophilic polyamide copolymers, such as the copolymers of caprolactams and an alkylene oxide diamine and copolymers of hexamethylene adipamide and alkylene oxide, as well as mixtures and copolymers thereof. Suitable polyesters include polyethylene terephthalate, polybutylene terephthalate, polycyclohexylenedimethylene terephthalate, and mixtures and copolymers thereof. Acrylic copolymers suitable for the present invention include ethylene acrylic acid, ethylene methacrylic acid, ethylene methacrylate, ethylene methacrylic acid, ethylene methacrylate, ethylene ethyl acrylate, ethylene butyl acrylate and mixtures thereof. Among the various combinations of the suitable component polymers illustrated above, due to economic availability and desirable physical properties, particularly suitable conjugate fibers contain a combination of different polyolefins having the melting point differential discussed above. More particularly suitable conjugated fibers are bicomponent polyolefin conjugate fibers having a polyethylene component, for example, a high density polyethylene, a linear low density polyethylene and mixtures thereof and a polypropylene component, eg, isotactic propylene. , syndiotactic propylene and mixtures thereof.

Suitable conjugate fiber configurations include the concentric sheath-core, eccentric sheath-core, island-in-sea, and side-by-side configurations. Conjugated fibers having symmetrically arranged component polymers are particularly suitable for the present invention. For example, the concentric sheath-core conjugate fibers, since the fibers having a symmetric polymer arrangement do not possess latent or potential rizability. In general, asymmetric conjugated fibers, such as side-by-side conjugated fibers, containing component polymers having different crystallization and / or shrinkage properties possess latent rizability, which can be thermally or mechanically activated. It is believed that latent rizability is imparted to the conjugate fibers due to the shrinkage disparity of the component polymers. When such conjugated fibers are exposed to a heat treatment or a pulling process, the disparity of shrinkage between the component polymers of the conjugate fibers during the heat treatment or the pulling process causes the fibers to be crimped. As such, when the fibers having an eccentric or side-by-side sheath-core configuration are used, the fibers require processing in a manner such as to prevent the fibers from possessing or activating a latent rippling. For example, U.S. Patent No. 4,315,881 issued to Nakajima et al. Describes a process for producing short polyethylene-polypropylene side-by-side conjugate fibers that do not have curls or latent rizability, the patent of which is incorporated herein by reference. reference. The process uses a specific stretch ratio and a temperature to obtain conjugate fibers without curls or latent rizability. As for the spunbonded conjugate fibers, the production process for the fibers can be adjusted to avoid ripples and latent rizability. For example, the conjugate fibers having polypropylene and polyethylene can be pulled with a high pulling tension during the spin-bonded fiber formation process, for example, by providing a low polymer production rate and increasing fiber pulling force. , to produce conjugated fibers that do not have curls or latent rizability.

A non-woven fabric suitable for the present invention, which has a relatively uniform fiber cover, can be formed by isotropically depositing the unriginated conjugated fibers on a forming surface. The nonwoven fabric bonded by deposited spinning of the conjugated fibers is carried on a foraminous support surface and then attached in a jointer via air. Figure 3 illustrates an example air-through-joinder 10 that is suitable for the present invention. The joiner 10 receives a non-woven fabric 12 disconnected on a foraminous support surface 14. The air joiner 10 is equipped with an adjustable temperature heated air source 16 which heats the air and directs the heated air towards the non-woven fabric. screen 12, and a vacuum apparatus 18 which is placed below the support surface 14 and directly below the heated air source 16. The vacuum apparatus 18 facilitates the heated air to move through the non-woven fabric 12. Unlike a hot or conventional air oven, or a radiant heater which applies heat only on the surface of the non-screening and rests on the thermal conductivity of the fabric to heat the interior of the fabric, a binding through air forces the air heated through the non-woven fabric to quickly and evenly raise the temperature of the fabric to a desired level. Although the flow rate of the heated air can be varied to accommodate the caliber and fiber density of each non-woven fabric, a speed of from about 100 feet per minute to about 500 feet per minute is highly desirable. The temperature of the heated air and the residence time of the non-woven fabric in the joiner are adjusted to heat the fabric to a temperature which is higher than the temperature of the melt, for example, the melting temperature peak determined with a DSC, of the polyolefin component of low melt, but lower than the melting point of the higher melt component polymer of the conjugate fibers. Desirably, the linker heats the fabric to a temperature that is high enough to melt at least about 50% of the olefin component polymer but not so high as to melt more than 10% of the higher melt component polymer, as defined by melt curves DSC. More desirably, the joiner heats the fabric to a temperature that completely melts the low melt polyolefin component but that melts less than about 10% of the higher melt component polymer, as defined by the polymer melt DSC curve. of higher melting component of the conjugate fibers. For example, when a non-woven fabric of bicomponent conjugated fibers having polypropylene and a linear low density polyethylene is used, the air-through-joiner desirably applies a flow of heated air having a temperature between about 260 ° F and about of 300 ° F, and the residence time of the fabric in the joiner is desirably between about 0.1 seconds and about 6 seconds. It should be noted that a short residence time in the joiner is highly desirable since any latent rizability that can be imparted during the fiber forming process, in general, does not manifest itself if the duration of the jointing is short. In addition, the flow rate of the heated air can be adjusted to control the caliper and porosity of the non-woven fabric. Generally, a higher flow rate produces a united fabric having a lower caliper and a lower porosity.

Unlike non-woven webs bonded by conventional calendering having non-uniform pore size and porosity distributions, as discussed above, the present air-bonded filter media provides a highly pore size and porosity distribution. improved and the medium does not contain mechanically compacted regions that impede the filtering function of the medium. further, unlike a calendering process that applies mechanical compaction pressure and alters the pore size and pore configuration of different sections of the non-woven fabric, depending on the caliber of the different sections of the non-woven fabric, the The process of bonding through air in conjunction with the non-curled and non-curling nature of the present conjugated fibers allows the non-woven fabric to join without imparting significant non-uniform changes in the pore size and in the configuration of the non-woven fabric.

An additional advantage of the present nonwoven filter medium is that the porosity and density of the filter medium can be controlled not only with conventionally known approaches, for example by varying the basis weight of the filter medium and varying the thickness of the filter media. conjugated fibers, but also during the joining process. The polymer selection criterion, especially the melting point criterion, of the present invention provides an additional approach that can conveniently be used to control the porosity and density of the filter medium. As discussed above, because the difference in melting point between the low melt and high melt component polymers of the conjugate fibers, the non-woven fabric produced from the fibers can be exposed to a temperature that is not only high enough to melt the low melt component polymer but it is also high enough to allow the melt viscosity of the melted polymer to be lowered so that the melted polymer extends while preserving the physical integrity of the higher melt component polymer and of the non-woven fabric. In general, a binding temperature that is measurably higher than the temperature at which the low melt polyolefin component melts completely facilitates and induces the spreading of the melted polyolefin, thereby reducing porosity and increasing the density of the non-woven fabric . It can be noted that the present high density filter medium has a low caliper and a high abrasion resistance which are highly suitable for processing the medium within a highly folded filter medium.

As a further embodiment of the present invention, the porosity and density of the nonwoven filter media can also be controlled by varying the level of the melted polyolefin content under the conjugate fibers. Generally, conjugated fibers having a higher level of low melt polyolefin content form a nonwoven filter medium having lower porosity, higher density and superior abrasion resistance. In addition, the porosity and caliber of the nonwoven filter media can be controlled during the bonding process by adjusting the flow rate of the heated air. Generally, a higher heated air flow rate produces a bonded filter medium having a lower caliper and a lower porosity.

The present filter medium is therefore illustrated here with a single layer medium. However, the filter medium can have more than one layer. For example, the conjugate fiber filter medium of the present invention having different fiber thicknesses and / or densities can be laminated or deposited sequentially and then joined to form a filter having a porosity gradient. Additionally, the conjugate fiber filter medium can be laminated to a microfiber filter media.

Even though the filter medium is illustrated in conjunction with liquid filtering applications, the medium is highly suitable for gas filtering applications. In addition, for gas filtering applications, the density of the filter medium may still be higher in order to increase the efficiency of the filter medium. Even when the production capacity of such a high density filter medium is low, the production of the medium can be accommodated by three-dimensionally forming or folding the filter medium since as discussed above, the filter medium is highly thermoformable. The folded filter medium has an increased effective filtering surface area and therefore has an increased production rate.

Accordingly, the filter medium for gas filtration can have a density of up to about 0.5 g / cm3, desirably between about 0.1 g / cm3 and about 0.5 g / cm3, more desirably of between about 0.11 g / cm3. cm3 and about 0.45 g / cm3, more desirably between about 0.12 g / cm3 and about 0.4 g / cm3.

The non-woven fabric filter medium of the present invention can be easily thermoformed into three-dimensional shapes without measurably changing the porosity and physical properties of the medium. The non-woven fiber fabric conjugated to the present filter medium can be thermoformed immediately after the fabric is bonded through air but before the fabric cools since the bonded fabric coming out of the union through air is highly folding. Consequently, the uncooled fabric can be handled in untreated ways before the fabric cools to retain the applied shape. For example, the uncooled fabric can be folded using a known folding process. Figure 4 illustrates an example of a suitable folding process. The fabric 52 can be passed through a set of intermeshing pleating plates or pressed between two intermeshing bending plates 54 and 56, which have wedges of equal length perpendicularly clamped and equally spaced 58, and then cooled to solidify the polymer. low melted polyolefin while the fabric is retained in the folding plates to permanently seat the folding configuration within the non-woven fabric.

The conjugate fiber filter medium is a highly abrasion resistant and self-supporting filter medium which has a high filter efficiency and desirable strength properties. As such, the present filter medium is highly suitable for large volume liquid filtering applications. The filter medium can be used as a roll filter means, which is continuously supplied to a filtering device, for example, a flat bed filter, or as a sheet filter means. The filter medium can also be adjusted in a filter frame.

The filter medium can also be electrostatically treated in a convenient manner to form an electret filter medium and is highly thermoformable without sacrificing the physical and electret properties of the medium. Accordingly, the non-woven filter medium is highly suitable for forming three-dimensional filter media in a thermoformer apparatus and for forming high-folded density filter media. The three-dimensional thermoformed filter media, which are firm and self-supporting, can be easily fitted within a conventional filter housing or frame in a conventional manner. The filter media is highly suitable for various filtration applications. More particularly, the filter means are highly useful for liquid and gas filtering applications including water filters, oil filters, various gas filters and the like; and electrostatically treated filter media are particularly suitable for gas filtering applications including industrial air cleaner filters, HVAC filters, automotive air filters, vacuum cleaner filters, and the like.

The following examples are provided for purposes of illustration and the invention is not limited thereto.

Examples: The following test procedures were used to determine various properties of the filter media.

Filter Efficiency Test; The service life and efficiency of the filter samples were tested as follows. The filter test apparatus had a 90 mm diameter filter support assembly, which had an inlet and an outlet and directed the influent fluid entering from the inlet to pass through the sample filter medium, a pump and a regulator / flow meter unit, which supplies the influent fluid to the filter support assembly and is capable of maintaining a flow rate of 1.2 liters / min / cm2, and a pressure gauge, which is Place on the inlet side of the filter holder assembly. Samples of the filter medium were prepared by cutting the filter tissues to fit a filter holder 90 mm in diameter. Each filter medium was weighed and adjusted in the filter holder assembly. A test fluid, which contained 40 milliliters of an oil / soap emulsion QP 24 and 1200 milliliters of deionized water, was placed in a beaker and then 1 gram fine test particle AC was added to the test fluid. The test particles had the following particle size distributions: Size (less than) Volume% 5.5 μm 38 11 μm 54 22 μm 71 44 μm 89 176 μm 100.

The test fluid was continuously stirred with a magnetic stirrer and maintained at 38 ° C. The pump inlet was placed in the beaker, and the test fluid was pumped through the sample filter and then returned to the beaker, forming a continuous circuit, at a flow rate of 800 ml / min. Initial pressure and time were noted. The flow regulator was constantly adjusted to maintain a constant flow rate as the test particles accumulated on the test filter medium and the inlet pressure was increased. One gram of the test particles were added to the beaker at an interval of 5 minutes until the inlet pressure reached 2.1 kg / cm2, at which time the filter medium was considered clogged.

The clogging time was noted and the filter medium was removed. The removed filter media was weighed to determine the captured test particles after drying completely in an oven set at 180 ° F. The efficiency of the filter medium was determined by dividing the weight of the test particles captured by the weight of the total test particles added to the weeping vessel. This efficiency test determines the overall efficiency of the filter medium over its entire service life.

Initial Filter Efficiency: The initial filter efficiency measures the filter efficiency of the sample filter medium before a significant amount of the test particles accumulate on the medium, thereby measuring the inherent filter efficiency of the medium. For this efficiency test, the efficiency test procedure described above was repeated, except that the placement of the test was changed to an open circle system. 1240 milliliters of the test fluid described above, which contained 40 milliliters of oil / soap emulsion QP 24, 1200 milliliters of deionized water and one gram of the fine test particles AC, was passed through the test filter and then measured the efficiency of the filter.

Frazier Permeability: The Frazier permeability, which expresses the permeability of a fabric in terms of cubic foot per minute of air per square foot of medium to a pressure drop of 0.5 inches (1.27 centimeters) of water was determined using a permeability tester of Frazier air available from the Frazier Precision Instrument Company and was measured in accordance with Federal Test Method 5450, Standard No. 191A.

Density: The density of each filter medium was calculated from the basis weight and the gauge, which was measured at 35 g / cm2 with a Starret type volume tester.

Mullen Break: This test measures the resistance of a medium against a multidimensional stretching force. The test was conducted in accordance with ASTM D3786-87.

Example 1 (Exl) A non-woven low lift fabric of bicomponent conjugate fibers bonded by linear low density polyethylene sheath polypropylene sheath core was produced using two single screw extruders and a sheath-core spin pack. The bicomponent fiber contained 20% by weight of linear low density polyethylene (LLDPE) and 80% by weight of polypropylene. The LLDPE, Aspun 6811A, which is available from Dow Chemical, was mixed with 2% by weight of a Ti02 concentrate containing 50% by weight of Ti02 and 50% by weight of polypropylene, and the mixture was fed into a first extruder single screw The polypropylene, PD3443, which is available from Exxon, was mixed with 2% by weight of the Ti02 concentrate described above, and the mixture was fed into a second single screw extruder. Using a bicomponent spinning die, which had a spin hole diameter of 0.6 millimeters and a L / D ratio of 6: 1, the extruded polymers were spun into round bicomponent fibers having a concentric sheath-core configuration. The temperatures of the melted polymers fed into the spinning matrix were maintained at 232 ° C, and the spin hole production rate was 0.5 grams / hole / minute. The bicomponent fibers exiting the spinning matrix were cooled by an air flow having a flow rate of 45 cubic feet / minute / inch spinner organ width (0.5 m3 / min / cm) and a temperature of 65 ° F (18 ° C). The fibers entering the vacuum cleaner were pulled with the feed air at a flow rate of about 19 ft3 / minute / inch (0.21 m3 / min / cm). The weight-per-unit-length measurement of the pulled fibers was around 2.5 denier per filament. The pulled fibers were then deposited on a foraminous forming surface with the aid of a vacuum flow to form a first unbonded fiber fabric. An identical bicomponent fiber spinning unit was placed consecutively next to the first fiber spinning unit and deposited the pulled fibers on the first unbonded fiber fabric, forming a unitary unwoven fabric.

The unbound fiber fabric was bonded by passing the fabric over a foraminous support surface through a bond through air that applied a flow of air heated to a temperature of 138 ° C and at a rate of 500 feet / minute. (152 meters / minute). The residence time in the unit was around 2 seconds. The resulting nonwoven fabric had a basis weight of 102 g / m2 and had a uniformly bound sheet type configuration. The nonwoven filter media was tested for various properties as shown in Table 1.

Example 2 (Ex2) A low raised weave was produced from bicomponent conjugated fibers bonded by polypropylene-LLDPE sheath core spin according to the example, except that the weight ratio of the polypropylene LLDPE was 50:50. The results of the test are shown in Table 1.

Example 3 (Ex3) A non-woven raised fabric was produced from conjugated bicomponent side-by-side fibers of LLDPE and polypropylene having a weight ratio of 50:50. The production process delineated in Example 1 was repeated, except that the side-by-side spinning die was used to produce conjugate fibers having a side-by-side configuration. The feed air flow rate was increased to prevent the fibers from being curled and a latent rizability, and the flow rate was around 0.22 m3 / minute / cm width. The results are shown in Table 1.

Example 4 (Ex4) A non-woven fabric raised under the polypropylene sheath-nylon core 6 was produced according to the procedure outlined in Example 1, except that the binding air temperature was 149 ° C. The weight ratio between polypropylene and nylon 6 was 90:10. The nylon was obtained from Custom Resin and had a sulfuric acid viscosity of 2.2. The results are shown in Table 1.

Example 5 (Ex5) A high density filter medium of LLDPE sheath / nylon core 6 spun yarns was prepared according to example 4, except that the weight ratio between LLDPE and nylon 6 was 80:20. Example 5 is a comparative example for the purpose of illustration of the present sheet filter even though the filter means is highly suitable for folded filter applications. The results are shown in Table 1.

Example 6 (EX6) A high density filter medium of sheath / core spunbonded fibers of 80% by weight of LLDPE / 20% by weight of polypropylene was prepared according to Example 3. Example 6 is a comparative example for the purpose of The illustration of the sheet filter is present even though the filter medium is highly suitable for folded filter applications. The results are shown in Table 1.

Comparative Example 1 (Cl) A conjugated fiber fabric joined by spinning from side to side curled was prepared by repeating the production procedure of Example 3, except that the used suction air was heated to about 350 ° F and the flow rate was 23 ft3 / minute / inch wide. The unbound fiber fabric was bonded by passing the fabrics through a linker through air having an air temperature of 272 ° F and an air velocity of 200 feet / min. The results are shown in Table 1.

Comparative Example 2 (C2) A knit-bonded polypropylene spun fiber fabric was tested, which is commercially available from Kimberly-Clark under the Accord "** 0 *" brand and has a bonded area of about 25%, based on its filter efficiency. The results are shown in Table 1.

Comparative Examples 3-6 (C3-C6) Comparative examples 3 and 4 were the ReemayMARCA filters, style numbers 2033 and 2440, respectively. Reemay "* 0 * filters are calendered bonded fabrics of fibers bonded by polyethylene terephthalate polyester yarn and copolyester spunbonded fibers .. Comparative example 5 was Typar 3301, which is a non-woven fabric bonded by polypropylene spinning The Reemay "" 10 * and the Typar "* 0 * are commercially available from Reemay, Inc., of Old Hickory, Tennesee.

Comparative Example 6 was a commercial liquid filter medium available from Auchenbach, Germany. The filter medium is a non-woven fabric bonded by calendered polyester yarn which is bonded at the point with an acrylic binder. The results are shown in Table 1.

Comparative Example 7 (C7) A laminate of three unbound layers from Reemay 2011 was tested for initial filter efficiency. The Reemay 2011 was selected since the density of the material is within the range of the filter medium present. The results are shown in Table 1.

Table 1 ProDorción Perm. Efficiency Rctt ?? i-Tiiatto Example Polymers x Weight B. Weight Density Denier Frazier General Initial Life Mullen (% Weight) (g / m2) (g / cc) (%) (%) (min) Exl LLDPE: PP 20:80 102 0.08 2.1 61 36 19 24.7 6.6 Ex2 LLDPE: PP 50:50 102 0.11 2.5 54 31 23 12.8 5.4 Ex3 LLDPE: PP 50:50 102 0.12 2.5 61 37 19 13.9 4.8 Ex4 PP: N6 90:10 108 0.19 2.5 19 38 32 2.3 - Ex5 LLDPE: N6 80:20 102 0.37 2.5 13 24 49 0.8 -? X6 LLDPE: PP 80:20 98 0.29 2.5 22 34 28 1.5 - Cl LLDPE: PP 50:50 102 0.05 2.5 97 33 14 90 2.7 C2 PP - 102 0.15 - 21 - 20 - 7.0 C3 Polyester - 98 0.26 4 76 23 12 5.9 5.9 C4 Poliéter - 98 0.18 4 107 28 5 41.8 2.7 C5 PP - 102 0.33 10 46 20 2 38.5 6.5 C6 Polyester - 85 0.37 - 44 19 10 1.1 11.2 C7 Polyester 78 0.14 4 5 Note: B. Weight = Base Weight (g / m2) Perm Frazier = Frazier Permeability (m3 / minute / m2) Mullen Break in kilograms / cm2 The results clearly indicate that the filter media of the present invention exhibit a highly desirable combination of good filter efficiency, filter life and strength properties, especially for filtering liquids. Compared to the polypropylene and polyester spunbonded filter media of the prior art, the conjugate fiber filter media of the present invention has a combination of highly improved initial and general efficiencies, and filter life, as well as that provided high strength properties.

In addition, examples of the filter media present also demonstrate that the physical properties, e.g., density, permeability and strength, of the filter media can be easily modified by changing various elements of the manufacturing process of the media. filter. For example, by changing the weight ratio of the component polymers, changing the component polymers and / or changing the binding conditions, the filter media can be produced to have different physical and filtering properties.

In order to more clearly demonstrate the highly useful combination of efficiency and life of the present filter media, the filter efficiency data and the filter life data for examples 1-6 and comparative examples 3-5 were plotted , since the examples have a similar basis weight and therefore must be directly comparable. Figure 5 illustrates the filter efficiencies with respect to the densities of the example filter media; Figure 6 illustrates the filter life with respect to the densities of the filter medium; and Figure 7 illustrates the initial filter efficiencies of the example filter media.

Figure 5 illustrates that the filter efficiencies of the present filter media are significantly better than commercial polyester filter media; Figure 6 shows that the filter media present have a long service life; and Figure 7 shows that the filter media present have a highly improved initial filter efficiency. It should be noted that while the filter life of the commercial polyester filter media may appear beneficial from Figure 6, Figure 5 and Figure 7 clearly demonstrate that the extended life of these filter media is the result of an efficiency of poor filter. Declared in alternating form, the commercial filter media allow a large part of the polluting particles to pass through the media and, therefore, decrease the accumulation of the contaminant cake on the filter surface, extending the service life still when providing a poor filter efficiency.

From Figures 5 and 6, it can be seen that, for liquid filtering applications, the filter media present provide an especially desirable combination of filtration efficiency and life when the media have a density of between about 0.07 g / cm3 and around 0.2 g / cm3.

As can be seen from the foregoing, the air-bonded conjugate fiber filter media of the present invention has highly desirable filter attributes such as similar filter efficiency, strength and life. Accordingly, the filter media is highly useful for various filtering applications that require filter attributes including self-support, high efficiency, long filter life and resistance.

Claims (20)

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

1. A filter medium comprising autogenously bonded, non-crimped conjugate fibers, said medium having a density of between about 0.07 g / cm 3 and about 0.2 g / cm 3 and a Frazier permeability of at least 15 m 3 / min / m 2, said Conjugated fibers comprise a polyolefin and a second thermoplastic polymer having a melting point higher than said polyolefin, wherein said medium has a breaking strength Mullen of at least about 3.5 kg / cm2.

2. The sheet filter medium, as claimed in clause 1, characterized in that said second thermoplastic polymer has a melting curve of differential temperature calorimetry analysis higher than the polyolefin so that an exposure to a temperature that melts around 50% of said polyolefin melts equal to or less than about 10% of said thermoplastic polymer.

3. The sheet filter means, as claimed in clause 2, characterized in that said polyolefin and said second thermoplastic polymer have melting curves of completely separate differential calorimetry analysis.

4. The sheet filter means, as claimed in clause 1, characterized in that said polyolefin is selected from polyethylene, polypropylene, polybutylene, polypentene and mixtures and copolymers thereof.

5. The sheet filter means, as claimed in clause 1, characterized in that said second thermoplastic polymer is selected from polyolefins, polycarbonates, polyamides, polyesters, acrylic copolymers, and mixtures and copolymers of. the same.

6. The sheet filter means, as claimed in clause 1, characterized in that said polyolefin is a linear low density polyethylene and said second thermoplastic is polypropylene.

7. The sheet filter means, as claimed in clause 1, characterized in that said polyolefin is a linear low density polyethylene and said thermoplastic is nylon 6.

8. The sheet filter means, as claimed in clause 1, characterized in that said polyolefin is a linear low density polyethylene and said second thermoplastic is a polyethylene terephthalate.

9. The sheet filter means, as claimed in clause 1, characterized in that said means is connected through air and is without mechanically compacted regions.

10. The sheet filter means, as claimed in clause 1, characterized in that said medium has a density between about 0.08 g / cm3 and about 0.19 g / cm3.

11. The sheet filter means, as claimed in clause 1, characterized in that said medium has a Mullen breaking strength of at least about 4 kg / cm2.

12. The sheet filter means, as claimed in clause 1, characterized in that said conjugate fibers are conjugated fibers joined by spinning.

13. The sheet filter means, as claimed in clause 1, characterized in that said means is formed three-dimensionally.

14. The sheet filter means, as claimed in clause 1, characterized in that said conjugated fibers are spunbonded fibers and said polyolefin and said second thermoplastic polymer have melting curves of different differential calorimetric analysis so that an exposure at a temperature that melts about 50% of said polyolefin melts equal to or less than about 10% of said thermoplastic polymer.

15. A filter medium comprising autogenously bonded non-crimped conjugate fibers, said filter means having a density of between about 0.07 g / cm3 and about 0.5 g / cm3 and being thermoformed three-dimensionally, said conjugate fibers comprise a lower melt polyolefin and a superior melt polymer as defined by melt curves of calorimetry analysis, wherein an exposure to a melting temperature of about 50% of said lower melt polyolefin melts equal to or less than about 10% of said polymer melted superior.

16. The sheet filter means, as claimed in clause 15, characterized in that said polyolefin is selected from polyethylene, polypropylene, polybutylene, polypentene, and mixtures and copolymers thereof.

17. The sheet filter means, as claimed in clause 15, characterized in that said higher melting polymer is selected from polyolefins, polycarbonates, polyamides, polyesters, acrylic copolymers and mixtures and copolymers thereof.

18. The sheet filter means, as claimed in clause 15, characterized in that said polyolefin is linear low density polyethylene and said higher melting polymer is polypropylene.

19. The sheet filter means, as claimed in clause 15, characterized in that said medium has a density of between about 0.1 g / cm3 and about 0.5 g / cm3.

20. The sheet filter means, as claimed in clause 15, characterized in that said conjugated fibers are fibers joined by spinning. SUMMARY The invention provides a sheet filter means having autogenously bonded non-crimped conjugated fibers which contains a polyolefin and another thermoplastic polymer having different melting points. The filter medium has a density between about 0.07 g / cm3 and about 0.2 g / cm3. The invention further provides a three-dimensionally thermoformed filter medium having a density of between about 0.07 g / cm3 and about 0.5 g / cm3.