MXPA98004552A - Zonific hot air blade - Google Patents

Abstract

The present invention relates to a zoned heated air knife assembly and a process includes a plurality of spaced discrete spaced air blades which is useful for inter-filament bonding of non-woven fabrics, for thermal bonding of the laminates including non-woven fabrics, and other applications. The zoned air knife assembly and process facilitates the manufacture of low density non-woven fabrics from low bonding areas and laminates having high structural integrity. The zoned heated air knife also reduces the amount of heated air and, therefore, the energy required for the production of non-woven fabrics and thermally bonded laminates.

Description

BLADE D? HOT AIR ZONED FIELD D? THE INVENTION This invention is directed to a hot air blade assembly useful in the production of fabrics bonded with very low density yarn, as well as nonwoven laminate structures bonded by spinning / melt-drying / spin-bonding, and carded fabrics attached . More particularly, this invention is directed to a zoned hot air knife assembly having a plurality of spaced apart areas. This invention also includes a method for producing fabrics bonded with yarn that are not significantly compacted or pre-bound.

BACKGROUND OF THE INVENTION Non-wovens are the fabrics that constitute all or part of numerous commercial products such as adult incontinence products, sanitary napkins, disposable diapers and hospital suits. Non-woven fabrics or fabrics have a physical structure of individual fibers, threads or fibers which are interlocked, but not in a regular and identifiable manner as in a woven or woven fabric. The fibers may be continuous or discontinuous, and are frequently produced from polymer resins or thermoplastic copolymers of the general classes of polyolefins, polyesters and polyamides as well as numerous other polymers. Mixtures of the polymers on the multi-component conjugate fibers can also be used. The methods and apparatus for forming the fibers and producing a non-woven fabric of synthetic fibers are well known, common techniques include meltblowing, spinning and carding.

Non-woven fabrics can be used individually or in composite materials such as in a meltblown / meltblown (SM) laminate or in a three-ply fabric bonded with spinning / meltblown / spunbonded (SMS). They can also be used in conjunction with films and can be joined, recorded, treated or colored. Colors can be achieved by adding an appropriate pigment to the polymeric resin. In addition to the pigments, other additives may be used to impart specific properties to the fabric, such as the addition of a fire retardant to impart flame resistance or the use of a particular inorganic material to improve porosity. Because they are made of polymeric resins such as polyolefins, the non-woven fabrics are usually extremely hydrophobic. In order to make these materials wettable, the surfactants can be added internally or externally. In addition, additives such as wood pulp or fluff can be incorporated into the fabric to provide increased absorbency and decreased fabric density. Such additives are well known in the art. The bonding of the non-woven fabrics can be achieved through a variety of methods typically based on heat and / or pressure, such as through bonding with air and thermal bonding. Ultrasonic bonding, hydroentanglement and stitching can also be used. There are numerous engraving and bonding patterns that can be selected with respect to physical properties, texture and appearance.

The qualities of such resistance, softness, elasticity, absorbency, flexibility and ability to breathe are easily controlled in the manufacture of nonwovens. However, certain properties must balance against others. An example will be an attempt to lower costs by decreasing the base weight of the fabric while maintaining a reasonable resistance. Non-woven fabrics can be made to feel like cloth type or plastic type as desired. The average base weight of fabrics not used for most applications is generally between 5 grams per square meter and 300 grams per square meter, depending on the desired end use of the material.

Non-woven fabrics have been used in the manufacture of personal care products such as disposable infant diapers, training pants for children, feminine pads and incontinence garments. Non-woven fabrics are particularly useful in the field of such disposable absorbent products because it is possible to produce them with a low-cost fabric-like aesthetic. Non-woven personal care products have been widely accepted by the consumer. The elastic properties of some non-woven fabrics have allowed them to be used in the form of garments for adjustment, and their flexibility allows the wearer to move in an unconstrained and normal manner. This combination of properties has also been used in materials designed to treat injuries; an example of such a commercially available product is the Kimberly-Clark FlexusMarca wrap. This wrap is effective in providing support for injuries without causing discomfort or complete constriction. SM and SMS laminate materials combine the qualities of strength, vapor permeability and barrier properties; Such fabrics have proven to be ideal in the area of protective clothing. Sterilization of surgical gowns and wraps made of laminated fabrics are widely used because they are medically effective, comfortable and their cloth-like appearance familiarizes patients with a potentially alienating environment.

Various mechanisms have been employed to increase the integrity of non-woven fabrics such as filament cloths joined by spinning. A known method is the corapactation, in which the fabric is passed between the heated or unheated pressure point rolls to cause an interfile joining. Another known mechanism is the hot air blade. A hot air knife is useful for joining the individual polymer filaments together at several places, so that the fabric has an increased structural integrity strength. Hot air blades are also used to align blowing fibers with melting during the manufacture of meltblown fabrics, to cut non-woven fabrics, to cut the garment, and for a variety of other uses.

One use of the hot air blade is to improve the structural integrity of the non-woven fabrics before passing them through the standard interlayer joining processes. The air bond (" ") is a bonding process of a non-woven bicomponent fiber fabric in which air that is hot enough to melt one of the polymers of the fabrics of the fabric is forced through the fabric. The air speed is between 100 and 500 feet per minute and the residence time can be as long as 6 seconds. The melting and resolidification of the polymer provides the bond. The union through air has a restricted variability and since the union through air requires the melting of at least one component to achieve this union, this is more effective when applied to fabrics 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 the other component is directed from a surrounding cover, through the fabric and up to a perforated roller that holds to 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 bonds between the filaments to integrate the fabric.

The air-binding process requires that the fabric has an initial structural integrity sufficient to hold the tissue together during bonding through air. The hot air blade has been used to provide non-woven fabrics (eg, spun-bonded fabrics) with initial structural integrity prior to bonding through air. However, a conventional hot air blade which exposes the entire fabric to the pre-bond can undesirably increase the density and reduce the thickness of the non-woven fabric.

A conventional hot air blade includes a mandrel with slots that blow a hot air liner over the surface of the nonwoven fabric. U.S. Patent No. 4,567,796 issued to Kloehn et al. Discloses a hot air blade which follows a programmed path to cut the shapes necessary for particular purposes, such as leg holes in disposable diapers. . United States Patent Application No. 08 / 362,328 to Arnold et al., Filed December 22, 1994, discloses the use of a hot air knife to increase the integrity of a spunbonded fabric. Figure 1 shows an exemplary hot-air knife in cross-section The hot air is supplied from a plenum 31 through a groove 2 on a nonwoven fabric (not shown) Typically, the length of the groove 2 (e.g. , in a direction perpendicular to the paper) will be at least as large as the width of the non-woven fabric being treated.

Although hot air blades may have been useful in many areas, these are applications in which the bulkier non-woven materials of lighter weight will be desirable from the standpoint of cost savings, aesthetic appearance and / or performance. One way to lower the density of a spunbonded fabric, for example, is to decrease the amount of bond between the individual filaments.

SYNTHESIS OF THE INVENTION The present invention is directed to a hot air knife assembly and to a process for thermally increasing the integrity of a nonwoven polymer fabric. A non-woven fabric is passed under a plurality of spaced-apart and spaced hot air knife zones which allow the jet of hot air at a multiplicity of spaced apart discrete locations across the width of a non-woven fabric. By breaking the hot air into a plurality of smaller, spaced apart jets, it becomes possible to apply the hot air in a pattern which exposes a much smaller percentage of the air of non-woven fabric to the hot air used to join, cut or other purposes The invention allows the production of spin-bonded non-woven fabrics having lower percentage binding areas, and consequently, lower bulk densities, than what can be achieved by using a conventional hot air knife across the width of the fabric.

Preferably, the spaced and spaced jet zones can be moved laterally between the side edges of the non-woven fabric, allowing application of the hot air in a wave, sinusoidal, or other non-linear pattern as the fabric moves in a direction of travel. machine under the hot air knife.

By using the hot air knife of the invention, discrete narrow columns of hot air can be applied in an unbonded fabric, creating a high integrity in the machine direction of "treading lines". These high-integrity tread lines eliminate the need for fabric compaction or hot-air stamping of 100% of the fabric, in order to achieve high integral lining.

With the foregoing in mind, it is a feature and an advantage of the invention to provide a process for increasing the integrity of a non-woven fabric which uses a hot air knife assembly having a plurality of spaced hot air knife zones. and separated.

It is also a feature and an advantage of the invention to provide a process for pre-bonding a non-woven fabric prior to bonding through air, the process of which increases the integrity of the non-woven fabric without significantly increasing its overall density or lowering its overall thickness .

It is also a feature and an advantage of the invention to provide a method for applying hot air which achieves a high integrity interlining joint, but lowers the overall bond area in a nonwoven fabric.

The foregoing and other features and advantages of the invention will become more apparent from the following detailed description of the present preferred embodiments, read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION D? THE DRAWINGS Figure 1 is a cross-sectional view of a conventional hot air knife as described above.

Fig. 2 is a perspective view of a process for joining a filament fabric bonded with yarn, using the hot air knife assembly of the invention that supplies a plurality of spaced apart hot air blades.

DEFINITIONS • As used herein, the term "nonwoven fabric or fabric" means a fabric having a structure of individual fibers or threads which are interleaved, but not in an identifiable manner as in a woven fabric. Non-woven fabrics or fabrics have been formed from many processes such as for example, the processes of blown with fusion, the processes of union with spinning and the processes of tissue joined carding. The term also includes films that have been punched or otherwise treated to allow air to pass through. The basis weight of the non-woven fabrics is usually expressed in ounces of material per square yard (osy) or grams' per square meter (gsm) and the fiber diameters are usually expressed in microns (Note that to convert from osy to gsm, must multiply osy by 33.91).

As used herein, the term "microfibers" means fibers of small diameter having an average diameter of no more than about 75 microns, for example, having an average diameter of from about 0.5 microns to about 50 microns or more particularly, microfibres which can have an average diameter of from about 2 microns to about 40 microns.

As used herein, the term "spunbonded fibers" refers to fibers of small diameter which are formed by extruding melted thermoplastic materials as filaments from a plurality of usually circular and thin capillaries of a spinner with the diameter of the extruded filaments being rapidly reduced as by, for example, in U.S. Patent No. 4,340,563 issued to Appel et al., U.S. Patent No. 3,692,618 issued to Dorschner and others, U.S. Patent No. 3,802,817 to Matsuki et al., U.S. Patent Nos. 3,338,992 and 3,341,394 to Kinney, the United States Patent No. 3,502,763 issued to Hartman, United States Patent No. 3,502,538 issued to Petersen, and United States Patent No. 3 .542,615 granted to Dobo and others. The yarn-bound fibers are cooled and are not generally sticky when they are deposited on a collecting surface. Spunbonded fibers are generally continuous and have average diameters greater than 7 microns, often between 10 and 20 microns.

As used herein, the term "spunbond" refers to a non-woven mat composed of spunbonded fibers.

As used herein, the term "melt blown fibers" means fibers formed by extruding a melted thermoplastic material through a plurality of usually circular and fine capillary matrix vessels such as yarns or yarns. • melted filaments inside gas streams heated at high velocity (eg, air) which attenuate the filaments of melted thermoplastic material to reduce its diameter, which can be to a microfiber diameter. Then, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a meltblown fabric of randomly dispersed melt. Such a process has been described, for example, in United States Patent No. 3,849,241 issued to Butin. Melt-blown fibers are microfibers which may be continuous or discontinuous, are generally less than 10 microns in diameter and are generally self-supporting when deposited on the collecting surface.

As used herein, the term "meltblown fabric" refers to a non-woven mat made of meltblown fibers.

As used herein, the term "polymer" generally includes but is not limited to homopolymers, copolysers, such as, for example, graft block copolymers, random and alternating, thermopolymers, etc. and mixtures and modifications of the same. same. In addition, unless specifically limited otherwise, the term "polymer" will include all possible geometric configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic and atactic 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 "transverse direction of the machine" or CD means the width of the fabric, for example, an address generally perpendicular to the direction of the masque.

As used herein, the term "bicomponent" refers to fibers which have been formed from at least two extruded polymers from separate extruders but spun together to form a fiber. Bicomponent fibers are also sometimes referred to as multicomponent or conjugated fibers. The polymers are usually different from each other even though the bicomponent fibers can be made from fibers of the same polymer. The polymers are arranged in areas placed essentially differently across the cross section of the bicomponent fibers and extend continuously along the length of the conjugate fibers. The configuration of all bicomponent 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 an arrangement of "islands in the sea". The bicomponent fibers are taught in U.S. Patent No. 5,108,820 issued to Kaneko et al., U.S. Patent No. 5,336,552 issued to Strack et al. And the U.S. Patent. United States No. 5,382,400 issued to Pike et al. For the two component fibers, the polymers may 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 polymers extruded from the same extruder as a -mix. The term "mixture" is defined below. The biconstituent fibers do not have the various polymer components arranged in different zones placed relatively constant across the cross-sectional area of the fiber and the various polymers are usually not continuous along the length of the fiber, instead of this, these usually form fibrils or protofibrils which start and end at random. Biconstituent fibers are sometimes referred to as multi-constituent fibers. Fibers of this general type are discussed in, for example, U.S. Patent No. 5,108,827 issued to Gessner. Bicomponent and biconstituent fibers are also discussed in the text Polymer and Compound Mixtures by John A. Manson and Leslie H. Sperling, copyright 1976 by Plenum Press, a division of Plenum Publishing Corporation of New York, IBSN 0-306 -30831-2, pages 273 to 277.

As used herein, the term "mixture" means a combination of two or more polymers while the term "alloy" means a subclass of mixtures where the • Components are immiscible but have been made compatible. The "miscibility" and the "immiscibility" are defined as mixtures having negative and positive values respectively for the free energy of mixing. In addition, "compatibilization" is defined as the process of modifying the interfacial properties of an immiscible polymer mixture in order to make an alloy.

As used herein, the term "hot air blade" refers to a device through which the stream of heated air under pressure can be emitted and directed. With such a device, it is also possible to control the air flow of the resulting jet of heated air. A conventional hot-air knife is described in United States of America patent application serial No. 08 / 362,328 filed December 22, 1994 and in United States Patent No. 4,567,796 issued February 4, 1986; both of which are incorporated herein by reference in their entirety.

As used herein, the term "composite" or "composite material" refers to a material which is composed of one or more layers of nonwoven fabric combined with one or more other layers of fabric or film. The layers are usually selected for different properties that these will impart to the general compound. The layers of such composite materials are usually secured together through the use of adhesives, entanglement or bonding with heat and / or pressure.

DETAILED DESCRIPTION OF CURRENTLY PREFERRED INCORPORATIONS Referring to Figure 2, a hot air knife assembly 10 includes a head 12 which is supplied with hot air through the inlet channels 14 and 16. The head 12 is of the shaped type as an elongated hollow cylinder having the ends 18 and 20 and the main body 22. The hot air supply channels 14 and 16 feed the air into the ends 18 and 20 of the head 12, as shown by the arrows.

The hot air supplied to the head 12 can have a temperature of about 200-550 ° F, more generally about 250-450 ° F, more commonly around 300-350 ° F. The optimum temperature will vary according to the type of polymer, the basis weight and the line speed of the non-woven fabric 40 traveling under the hot air knife assembly 10. For a cloth bonded with polypropylene yarn having a basis weight of about of 0.5-1.5 ounces per square yard, and traveling at a line speed of about 1000-1500 feet per minute, a hot air temperature of about 300-350 ° F is desirable. Generally, the temperature of the hot air must be at or near (e.g., slightly above) the melting temperature of the resin being joined.

The preferred volumetric flow of the hot air being fed to each hot air blade from the head 12 will generally depend on the composition and weight of the fabric, the line speed, and the degree of bonding required. The air flow rate can be controlled by controlling the pressure inside the head 12. The air pressure within the head 12 is preferably between about 2-22 mm Hg), more preferably between about 4-10 inches of air. water (8-18 mm Hg). Of course, the volume of the hot air required to effect the desired level of the interfiber connection can be reduced by increasing the temperature of the hot air. Operating parameters such as line speed, hot air volume, and hot air temperature can be determined and adjusted using techniques known and / or available to persons of ordinary skill in the art.

In the embodiment shown in Figure 2, the head 12 is cylindrical, but this may be rectangular or otherwise. Numerous sizes and shapes for the head 12 can be employed, with the preferred size depending largely on the width of the non-woven fabric and the degree of bond required. The head 12 can be constructed of aluminum, stainless steel or any other suitable material.

Extending from the head 12 is six spaced and spaced hot air passages 24, 26, 28, 30, 32 and 34. The passages may be rigid or flexible, but are preferably made of a flexible material to allow adjustment and / or the movement. The conduits are each connected at one end to the head 12, and are connected at their other ends to six plenums 36, 38, 40, 42, 44 and 46. Each plenum engages a hot air knife slot, with the slots being labeled 48, 50, 52, 54, 56 and 58. The plenums and slots shown in Figure 2 may each have a cross section similar to that of Figure 1, and described above with respect to the prior art. The difference is that the hot air blades of the prior art comprise a single elongated plenum and a groove extending through the cloth, while the hot air knife assembly 10 of the invention is divided into a plurality of spaced plenaries. and separate and knife slots as shown in figure 2.

The hot air from the head 12 is preferably supplied to an approximately equal volume and at a speed equal to each of the conduits 24, 26, 28, 30, 32 and 34. This egalitarian division of the flow can be achieved in a simple manner by the ensure that the ducts are of equal dimensions and size and by which the air pressure is uniform at the entrances to the ducts. On the other hand, if a particular application requires feeding more or less air into some of the ducts than others, different flow rates can be achieved by actuating valves individually in the ducts, by designing them with different sizes or through Full valves as explained below.

The plenums 36, 38, 40, 42, 44 and 46 are mounted on a sliding support bar 60. The plenums are mounted so that the lower tips of the hot air blades 48, 50, 52, 54, 56 and 58 are at a predetermined distance above the non-woven fabric 40. The distance between the air knife slots and the non-woven fabric should be about 0.25 to about 10 inches preferably about 0.75 to about 3.0 inches, more preferably from about 1.0 to about 2.0 inches. Preferably, the plenums are adjustably mounted on the support bar 60 so that the distance between the knife grooves and the fabric can be varied according to the needs of the application.

A control panel 62 is provided on one side of hot air blade assembly 10, incorporating the individual flow controls for the hot air that enters the plenums. As shown, the plenums are provided with individual flow control valves 64, 66, 68, 70, 72 and 74 which can be used to individually adjust the air flow to each plenum. The flow control valves can be electronically linked to the individual controls in the control panel 62 using conventional techniques available to those skilled in the art. As explained above, it is often desirable to have an approximately equal air flow for each of the plenums. The valves can be used for fine adjustment and equalization of the air flows to the plenums, or to differentiate between them if different flows are desired.

The non-bonded non-woven fabric 40 is carried on a worm conveyor including a carrier grid 77 carried by the rollers (one of these at point 76) at a predetermined line speed. The woven fabric 40 is moved in a machine direction (indicated by the arrow 78) under the hot air knife assembly 10, at a rate of generally around 100-3000 feet per minute, it is not commonly around of 500-2500 feet per minute, desirably from about 1000-2000 feet per minute. The hot air blade slots 48, 50, 52, 54, 56 and 58 apply hot air jets to the non-woven fabric, causing a localized bond to occur between the non-woven fabric filaments, at spaced apart locations. The separate and spaced joint causes the formation of "rolling lines" representing the joined areas 80, 82, 84, 86, 88 and 90. In the embodiment shown, the running lines are linear. In another embodiment, the support valve 70 is in communication with an oscillator (not shown) which causes the support bar 60 to move back and forth in the transverse direction (e.g., perpendicular to the machine direction). ) when the non-woven fabric 40 is brought forward in the machine direction. By using an oscillator, the rolling lines 80, 82, 84, 86, 88 and 90 can be formed in a wave-type pattern including without limitation sinusoidal waves, triangular waves, square waves, trapezoidal waves, or irregular waves.

The thickness of the rolling lines 80, 82, 84, 86, 88 and 90 corresponds to the lengths of the air knife slots 48, 50, 52, 54, 56 and 58. Generally, the running lines are so narrow as possible, to minimize the compaction and densification of the non-woven fabric. The air knife assemblies may each have a length of less than about 1.0 inches, preferably less than about 0.5 inches, more preferably about 0.10-0.25 inches. The length of the air knife slots will correspond essentially to the width of the regions joined in the fabric 40. The lengths of the air knife slots (eg, perpendicular to the movement of the fabric) can be determined based on the overall percentage of desired joined area. When the hot air knife slots are used to pre-screen a non-woven fabric, the area of the fabric covered by the pre-bond should be less than about 10% of the area of non-woven fabric, preferably around 1-5% of the nonwoven fabric area, more preferably of about 2-3% of the area of non-woven fabric.

The width of the openings in the hot air knife slots 48, 50, 52, 54, 56 and 58 (for example, the width of the opening as shown in Figure 1) must be configured to give the desired speed and of the air jets sticking on the surface of the fabric 40. The actual velocity of the air jets was determined by the air pressure inside the head 12, the total number of air knife slots, the lengths of the slots of air knife, and the widths of the hot air knife slots. The desired air blast velocity from the air knife slots is any speed required to cause a proper bond between the filaments of non-woven fabric. Generally, the width of each air knife slot opening (eg, parallel to the direction of movement of the fabric) should be about 0.5 inches or less.

The number of spaced apart air knife plenums and grooves may vary according to the width of the nonwoven fabric being treated as in the lengths of the individual air knife grooves. The larger the number of plenums and slots, the greater the maximum width of the tissue that can be effectively treated. Usually, the hot air blade assembly 10 should include at least two spaced apart air knife plenums and slots, when the nonwoven fabric 40 has a width of about 14-16 inches. Non-woven fabrics can have widths of up to 140 inches or greater, and the desired number of air knife plenums can be increased with the width of the non-woven fabric. As explained above, the air knife assembly 10 shown in Figure 2 includes six air knife slots and spacings spaced apart. The plenums may be spaced by from about 1-24 inches, but are preferably spaced from about 4-20 inches apart, more preferably from about 10-15 inches apart. Alternatively, the same effect can be created by providing a single slot opening extending across the width of the head 12, and blocking the portions of the slot opening to create the individual slot openings between the blocked regions.

The hot air knife assembly 10 of the invention makes it possible to produce non-woven fabrics with less binding between the filaments and correspondingly less density than conventional non-woven fabrics. The hot air knife assembly 10 is especially useful for the region of the yarn bonded fabrics not initially bonded as shown in Figure 2. As explained above, the hot air knife assembly 10 can be used to produce the fabrics bonded yarns in which the bond area within a filament constitutes less than about 10% of the total area, preferably less than about 5% of the total area of the fabric. Yarn-bonded non-woven fabrics produced with these low bond areas typically have a very low density compared to conventional yarn-bonded fabrics. The density of the non-woven fabrics produced using the hot air knife assembly 10 is generally less than about 0.075 grams / cc, preferably, less than about 0.045 grams / cc and may be as low as about 0.015. grams / cc. This density is measured under a load of 0.05 psi. A three-inch diameter plastic disc is attached to a pressure gauge and placed on a sample of the non-woven fabric under a pressure of 0.05 psi. The thickness of the fabric is then measured, and the density is calculated by dividing the thickness by the affected area of the sample.

The zoned air knife assembly of the invention can be used to increase the integrity of a wide variety of non-woven fabrics bonded with yarn. The fabrics can be, for example, constructed of a wide variety of polymers including without limitation polyamides, polyesters, ethylene and propylene copolymers, copolymers of ethylene or propylene with C4-C20 alpha-olefin, terpolymers of ethylene with propylene and copolymers of ethylene vinyl acetate alpha-olefin C4-C20, copolymers of propylene vinyl acetate, styrene-poly (ethylene-alpha-olefin) elastomers, polyurethanes, AB block copolymers wherein A is formed of poly (vinyl arene) moieties such as polystyrene and B is an elastomeric block medium such as a conjugated diene or a lower alkene, polyesters, polyether esters, polyacrylates, ethylene alkyl acrylates, polyisobutylene, polybutadiene, isobutylene-isoprene copolymers, and combinations of any of the foregoing. The fabrics can also be constructed of bicomponent or biconstituent filaments or fibers, as described above. The joining of the interlayers is effected by moving the nonwoven fabric 40 (FIG. 2) beneath the hot air knife slots 48, 50, 52, 54, 56 and 58, and is connected with the hot air jets preferably within about 15 degrees from the perpendicular to the fabric. As a consequence of the thermal energy imparted by the combination of the temperature, pressure and upper flow rates of the air jets, the non-woven fabric filaments are melted and merge together at the contact points corresponding to the lines connecting or "rolling" 80, 82, 84, 86, 88 and 90.

As explained above, the zoned hot air knife assembly is especially useful for producing the high integrity and low density pre-woven non-woven fabrics which are then passed through a conventional interfiber joining process. The union by air ( ) is a process of union of entrefibra whose effectiveness is helped by passing initially the non-woven fabric through the bonding process of hot air knife zonificado described above and illustrated in figure 2. Other Subsequent entanglement or bonding shapes may also be employed including, for example, thermal bonding, hydroentanglement, needle piercing, sewn bonding, and the like.

It is desirable that the number and lengths of the hot air blades (e.g., 48, 50, 52, 54, 56 and 58), as well as the process conditions are selected to provide a minimum increase in the overall density of the non-woven fabric 40. Desirably, the non-woven fabric 40 should have an average density after passing through the zoned hot air knife assembly that is within about 15% of the initial unbonded density, measured under a load of 0.05 psi. Preferably, the average prebonded density is within about 10% of the initial unbonded density, and is more preferably within about 7.5% of the initial unbonded density, measured under a 0.05 psi load.

The zoned hot air knife assembly and the process of the invention are also useful for other purposes. Other uses include, without limitation, the joining of layers in laminates of fabric joined with spinning / blowing with fusion or in laminates of fabric joined with spinning / blowing with melting / bonding with spinning, and in the production of carded and bound fabrics. The addition to provide an improved bond over a lower percentage area, the zoned hot air knife can be adjusted to melt and make films on the nonwoven or laminated fabric along the cut lines. This is achieved by applying upper velocity jets of a higher volume near the edges of the fabric. The film edges provide an inherent barrier which, for example, can be used to help prevent body fluids from draining off the sides of an absorbent structure including the fabric or the laminate.

The zoned hot air knife also provides the flexibility to create the channels in the machine direction generally in a laminate or non-woven fabric, having a variable width and depth to optimize the handling of the body fluid in the absorbent structures, the physical properties such as abrasion resistance in a covering, and / or aesthetic appearance in a wide variety of structures. In general, the zoned heated air knife also reduces energy requirements since only a small fraction of the laminate or nonwoven fabric is treated with the heated air.

In the production of laminates and meltblown fabrics, the conventional hot air knife joining process (covering 100% of the fabric) has a disadvantage in that it reduces the desirable barrier properties. During the production of the spunbond / meltblown / spunbonded web laminates, for example, the compaction rollers were sometimes used to regain these barrier properties. The zoned air knife assembly of the invention can overcome this reduction in barrier properties if the high integrity bond zones in the laminates are aligned with the slit lines (e.g., locations where the laminates are cut to form the final products) thus eliminating the need for compaction.

EXAMPLES 1-4 The samples of the polypropylene / polyethylene bicomponent fabric bonded with spinning were made with a spinning organ using the following process conditions, to give a fabric with the indicated properties: Polymer production: 0.6 grams / hole / minute Orifice density: 50 holes / inch Line speed: 60 feet per minute Base weight of the fabric: 2.5 oz. Per square yard Linear density of the fiber: 2.8 denier per filament Fiber composition: 50% polypropylene, 50% polyethylene in a side-by-side configuration Fabric width: 15 inches For Example 1, the fabric was not compacted or treated with a hot air knife. For Example 2, the fabric was compacted only using a standard compaction roller loaded at 64 pounds per linear inch and not treated with the hot air blade. For Example 3, the fabric was not compacted but treated with a conventional hot air knife covering the full width of the fabric. The hot air blade was placed about an inch above the conveyor carrying the fabric and tube a slot width of 0.375 inches, an air velocity of 2800 feet per minute and an air outlet temperature of 300oF.

For Example 4, a zoned hot air knife was used having three hot air blades spaced 3.5 inches apart each having a slot length of 0.25 inches, and a slot width of 0.375 inches. Again, each hot air blade is It placed about an inch above the conveyor and had an output air velocity of 2800 feet per minute, and an output air temperature of 300oF.

Subsequently, each fabric sample was subjected to a bonding process through air using an air velocity of 100 feet per minute and at a temperature of 260OF.

The following table shows the thickness (mils) of. Each fabric (measured under a zero load) in each phase of the process, and gives the resistance to the breaking of each fabric before joining. through air.

As shown above, the fabric of Example 1 (without hot air knife and without mechanical compaction) had a 'Fabric resistance unacceptably low before the bonding process through air, and showed a 65% decrease in thickness (under zero load) during the binding through air. The fabric of Example 2 (mechanically compacted only) had an acceptable fabric strength prior to bonding through air but showed a dramatic thickness reduction of 72.5% due to compaction, and a thickness reduction of 85% overall after of the union through air.

The fabric of Example 3 (complete hot air knife without mechanical compaction) had the acceptable fabric strength before bonding through air, but showed a large decrease of 62.5% in thickness due to the hot air knife and a reduction of Overall thickness of 77.5% after bonding through air. The fabric of Example 4 (hot air knife zoned, without compaction) was the only sample having an acceptable fabric strength before joining through air with only a minimum average thickness reduction (6.25%) before bonding to through 'air, due to the hot air blade. This fabric showed an average thickness reduction of 66.25% after bonding through air which is almost as good as the 65% reduction experienced with the fabric of Example 1 not having a pretreatment.

Although the embodiments described herein are currently considered to be preferred, various modifications and improvements may be made without departing from the spirit and scope of the invention. The scope of the invention is indicated by the appended claims and all changes that fall within the meaning and scope of equivalence are intended to be encompassed here.

Claims (29)

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

1. A method for increasing the integrity of a non-woven fabric or a laminate including the fabric, comprising the steps of: transporting the fabric or laminate in one direction of the machine along a conveyor; Y applying jets of heated air to the non-woven fabric in a plurality of spaced apart locations; the heated air jets being spaced apart and spaced in a direction transverse to the machine direction.

~~ 2. The method as claimed in clause 1, characterized in that at least three of the heated jets are applied to the non-woven fabric at spaced apart locations.

3. The method as claimed in clause 1, characterized in that at least five jets of heated air are applied to the non-woven fabric at spaced apart locations.

4. The method as claimed in clause 1, characterized in that at least six jets of heated air are applied to the non-woven fabric at spaced apart locations.

5. The method as claimed in clause 1, characterized in that the heated air jets supply air at a temperature of about 200-550oF.

6. The method as claimed in clause 1, characterized in that the heated air jets supply air at a temperature of about 250-450oF.

7. The method as claimed in clause 1, characterized in that the heated air jets supply air at a temperature of about 300-350oF.

8. The method as claimed in clause 1, characterized in that the heated air jets are supplied through less than about 10% of a width of the nonwoven fabric or laminate.

9. The method as claimed in clause 8, characterized in that the heated air jets are supplied through less than about 5% of the width of the fabric to a non-woven laminate.

10. The method as claimed in clause 8, characterized in that the heated air jets are supplied through less than about 3% of the width of the nonwoven fabric or laminate.

11. The method as claimed in clause 1, characterized in that the heated air jets are applied to the fabric to a nonwoven laminate in straight lines as the laminate or fabric passes under the jets.

12. The method as claimed in clause 1, characterized in that the heated air jets are applied to the nonwoven laminated fabric in a wave type pattern by passing the fabric or laminate under the jets.

13. A method for thermally bonding a non-woven fabric having an initially unbonded density and an average bonded density that is within about 15% of the initially unbound density, measured under a 0.05 psi load, the method comprising the steps of: transporting the fabric having the initially unbonded density in a direction of travel beneath a plurality of jets of heated air at locations spaced in a direction transverse to the direction of travel; and forming regions joined in the non-woven fabric using the hot air supplied from the heated air jets.

14. The method as claimed in clause 13, characterized in that the heated air jets are spaced apart by about 1-24 inches.

15. The method as claimed in clause 13, characterized in that the heated air jets are spaced and separated by about 4-20 inches.

16. The method as claimed in clause 13, characterized in that the heated air jets are spaced apart by about 10-15 inches.

17. The method as claimed in clause 13, characterized in that the joined regions each have a width of less than about 1.0 inches.

18. The method as claimed in clause 13, characterized in that the joined regions each have a width of less than about 0.5 inches.

19. The method as claimed in clause 13, characterized in that the joined regions each have a width of about 0.10-0.25 inches.

20. The method as claimed in clause 13, characterized in that the average bound density is within about 10% of the density not initially bound, measured under a load of 0.05 psi.

21. The method as claimed in clause 13, characterized in that the average bound density is within about 7.5% of the initially unbound density, measured under a load of 0.05 psi.

22. The method as claimed in clause 13, characterized in that the average bound density is less than about 0.075 grams / cc measured under a load of 0.05 psi.

23. The method as claimed in clause 13, characterized in that the average bound density is less than about 0.045 grams / cc measured under a load of 0.05 psi.

24. A method for joining a nonwoven fabric or laminate including the fabric, comprising the steps of: applying heated air jets to the nonwoven fabric in a plurality of spaced apart locations to cause thermal bonding of some of the filaments in the fabric. cloth; Y submit the laminated fabric including the fabric to a second joining process.

25. The method as claimed in clause 24, characterized in that the second joining process comprises the bonding through air of the non-woven fabric.

26. The method as claimed in clause 24, characterized in that the second joining process comprises the thermal point attachment of the non-woven fabric.

27. The method as claimed in clause 24, characterized in that the second joining process comprises the hydroentanglement of the non-woven fabric.

28. The method as claimed in clause 24, characterized in that the second joining process comprises the needle piercing of the non-woven fabric.

29. The method as claimed in clause 24, characterized in that the second joining process comprises the joint with firing of the non-woven fabric. SUMMARY A zoned heated air knife assembly and a process includes a plurality of discrete spaced apart air blades which is useful for the inter-filament bonding of the non-woven fabrics, for the thermal bonding of the laminates including the non-woven fabrics , and other applications. The zoned air knife assembly and process facilitate the manufacture of low density nonwoven fabrics with low bond area and laminates having high structural integrity. The zoned heated air knife also reduces the amount of heated air and, therefore, the energy required for the production of non-woven fabrics and thermally bonded laminates.