DE60317094T2 - Nonwoven fabric with high work capacity and manufacturing process - Google Patents

Description

FIELD OF THE INVENTION

The The present invention relates to a novel nonwoven fabric characterized by a high recovery, and relates to a method of preparation of the textile fabric using fibers of latent crimp.

BACKGROUND OF THE INVENTION

Nonwovens produced from thermoplastic synthetic fibers are well known in the art and find widespread commercial use under trademarks such as Tyvek ^® and Sontara ^® and the like, which are both available from the DuPont Company.

since For a long time, nonwovens are looking for a textile-like material High bulk product with high stretchability combined with high stray recovery. Such textile fabrics are collectively known as "stretch nonwovens". For the production of stretch nonwovens Many approaches are tried.

A of the approaches to producing stretch nonwoven fabrics been the use of crimped staple fibers, in which the entanglement of crimped fibers for the cohesion and provision provided that are needed in a stretch nonwoven fabric. In some cases were in the field crimp fibers too a mat and using an air or water jet to an interconnectedness. In other cases was in the art a smooth or largely smooth fiber with latent ripples first formed into a mat, after which the latent crimp was realized by heating, creating a "intricate" structure has been. However, the stretch nonwovens were more well-known execution toughness, which is defined as the product of tensile modulus and elongation at break, as well as Density to be used in numerous textile and technical applications be. It is the toughness of the textile fabric, which determines its "stretch ability" at which it is the amount by which it can be stretched, and about the force to its re-deformation. The Stretch nonwovens of known design are low density limited or, to use a technical term, on textile fabrics with high content with very low stretch.

Aranaga et al. reveal in the Japanese Patent Kokai Heisei 11-158733 a process in the hand lay-up process for producing a nonwoven fabric from a bicomponent fiber of polyethylene terephthalate / polypropylene terephthalate with latent crimping. The resulting nonwoven fabric should have a high percentage recovery. The wet laying process includes the step of hydroentangling the fibers to provide sufficient entanglement prior to development of the crimp. The nonwovens produced thereby are characterized by a basis weight of 30 g / m ² in a 0.3 mm thick textile fabric. It is recognized in Aranaga and elsewhere that high resiliency crimp fibers have the potential to produce high quality nonwovens. However, the acknowledgment acknowledged by Aranaga is that fibers with high restoring force tend to curl independently, resulting in an increase in the bulk of the fabric at the expense of reduced entanglement. This is often accompanied by a tissue break during shrinkage. The result is typically a high bulk fabric suitable for non-load-bearing applications where the full potential for a high-recovery fiber is not realized.

Furukawa disclosed in the US Patent No. 4469540 high loft nonwovens having a bulk density <0.020 g / cm ³ , which are made from crimped polyolefin bicomponent staple fibers. The crimp frequency of more than 4.7 crimps per centimeter (cm) (12 crimps per inch) is said to be detrimental to web production because it makes the web density excessively high. According to Furukawa, the structure should be "melt-bonded" by thermal bonding, and it is said to be this fusion bonding and less the fiber entanglement, which is the main mechanism by which the structure is held together.

Stokas et al. reveal in the WO 00/18995 a method of producing pressure-resistant Bausch nonwovens from crimped polyolefin bicomponent fibers, followed by crosslinking to preserve resilience.

Terakawa et al. reveal in the EP-A-0391260 B1 a method for producing nonwovens from Polyolefin bicomponent endless fibers wherein the spun yarn bundles have latent crimp and are air entangled, heated to a temperature at which the crimp develops and is heated to a temperature to effect bonding at the crossover locations. Terekawa nonwovens have densities below 0.030 g / cm ³ .

Shawver et al. reveal in the US Patent No. 5540976 made of spunbonded nonwoven stretch nonwoven fabrics, which is laminated to an elastomeric inner layer of a flat structure.

Pike et al. reveal in the US Patent No. 5418045 the production of a nonwoven web of thermoplastic multicomponent filaments with latent crimping and especially of polyolefins and crimped to varying degrees in air prior to the formation of a thermally bonded nonwoven web.

SUMMARY OF THE INVENTION

The present invention provides a nonwoven fabric comprising a plurality of intertwined, spirally-crimped asymmetric bicomponent fibers comprising a first crystallizable polyester component and having a second crystallizable polyester component, the first crystallizable polyester component exhibiting a slower crystallization rate than the second crystallizable polyester component and wherein the first crystallizable polyester component Fibers are characterized by a denier range of 0.5 to 5 denier, wherein the fibers exhibit at least 19.7 crimps per centimeter (50 crimps per inch) with a curling radius of curvature of 0.2 mm or less, and wherein the fibers are predominantly Furthermore, in which the fibers are further oriented predominantly in a well-defined plane of the nonwoven fabric, which is characterized by a bulk density of 0.2 to 0.4 g / cm ³ .

The present invention Further, a method for producing a nonwoven fabric, which method the deposition of a variety of asymmetric bicomponent fibers with latent ripples in a planar region of overlapping fibers, the fibers being predominantly oriented in the plane thereof; Arrange the planar area between two restrictive ones Surfaces; Heating the planar area to develop at least one Part of the latent ripples provided that during at least part of the heating the nonwoven structure itself in a limiting contact with the restrictive surfaces located.

BRIEF DESCRIPTION OF THE DRAWING

1 shows the wet fiber mat precursors and the fabric backing on the drying drum of the Williams pulp testing apparatus.

DETAILED DESCRIPTION THE INVENTION

It is known in the art to make nonwovens by preparing a planar region and typically a latent crimp bicomponent fiber mat, followed by heating to develop the crimp, thereby entangling the fibers to form a stable nonwoven structure. During the crimp development step, the fiber mats or other structures in the plane are subject to shrinkage while expanding in a direction perpendicular to the plane. As a result, the nonwoven fabrics of prior art usually have a relatively low bulk density well below 0.1 g / cm ^3. As a result, they have a limited utility in many textile applications where high toughness or high recovery is required.

The The present invention is based on the discovery that in formation a tangle under high crimping Fibers with high recovery capacity through a careful Control of the expansion of the textile fabric in one of the Plane of the textile fabric vertical direction during the Process of development of ripples can be stimulated. In the method of known design leads the Development of ripples usually to excessive shrinkage in the plane with simultaneous expansion in a perpendicular to the plane standing direction.

In the method of the present invention, in a first step, a plurality of latent crimp asymmetric bicomponent fibers are deposited to form a planar region of fibers, the fibers being predominantly oriented in the plane thereof, and wherein the majority of fibers are in cross-over contact with at least one of the other fibers is located. This pla In one preferred embodiment, the nare portion is referred to herein as a "fiber mat preform" to characterize a nonwoven fabric structure prior to being subjected to a second step of the process of the invention, namely, the crimp development step. The crimp development step is performed by heating the planar region to develop the crimp while placing the planar region between two constraining surfaces oriented at least approximately parallel to the plane of the planar region. The spacing of the two constraining surfaces is set such that during at least part of the crimp development step, the expansion of the planar region in a direction normal to the planar surface is limited by simultaneous contact with both constraining surfaces. This contact during the expansion step exerts a compressive force on the shrinking area. The resulting nonwoven fabric exhibits higher density and more robust physical properties than a nonwoven fabric made from a comparable starting material which is made without restricting expansion in a direction perpendicular to the planar surface.

For the procedure bicomponent fibers suitable for the present invention are fibers, comprising the two polymers and preferably from the same generic Family present in two phases of dispersion that are contiguous and wherein the two phases show a different shrinkage, whereby the development of spiral crimping during shrinkage is enabled. The phases can in a side-by-side arrangement or in an asymmetric one Sheath-core arrangement. Preferred is a side-by-side arrangement. Suitable bicomponent fibers shut down Bicomponent polyesters, bicomponent polyamides and bicomponent polyolefins, without being limited to these to be. Preference is given to polyesters. Included herein are copolymers of polymers within these broad classes. Preferred representatives bicomponent fibers among the polyesters include polyethylene terephthalate (PET) / polypropylene terephthalate (PPT), PET / polybutylene terephthalate (PBT) and PPT / PBT, with PET / PPT being preferred.

Of the Term "bicomponent" also includes Fibers, sometimes referred to as biconstituent fibers, this means have the polymers of different families, such as Polyamide and polyester. However, biconstituent fibers are less prefers.

For the tasks The present invention is a latent crimp fiber a fiber that is over itself an ability to develop an additional ripple using differences in shrinkage behavior which has two components, and typically by heating at least one of the components above its glass transition temperature. A fiber with latent crimping can some ripples or no ripples demonstrate. In the practice of the present invention, the fiber is with latent ripples preferably flat and without ripples.

The Inventors of the present invention have discovered that when the Development of a ripple under Conditions executed in which the expansion of the textile fabric in one to its level vertical direction takes place and is restricted, such as in that the crimp development step with the between two metal plates parallel to the plane of the fiber mat preform of the placed fabric is executed, the effect is that the textile fabric to a significant Compression is brought and the individual fibers are more closely entangled. The result is a denser, tenacious, textile fabric with improved recovery from a textile fabric, this with the aid of methods of known design starting with an identical Fiber mat preform is produced.

Of the Degree of compaction and the properties that can be achieved are from the curling contraction of the specific type of fiber used in the invention, and from the initial bulk density of the planar region, from the degree in which the fibers overlap one another and the separation distance between the restrictive ones Surfaces. Other things that are equivalent are a higher crimp contraction, a higher degree the overlap fibers among each other, one higher Initial bulk density and a narrower gap between restrictive ones surfaces (up to the point where the fiber can no longer slide and significantly hinders curling all) with a higher density nonwoven product, higher tenacity and higher Related to recovery.

The Uses from the process of the invention are quite general and leave for the production of nonwovens from almost any Use composition provided that bicomponent fibers with latent ripples in a planar area of overlapping fibers reach.

The fibers used in the invention are known in the form of Continuous fibers or in the form of long fibers, or they can Be staple fibers. Continuous fibers can be in the form of multifilament yarns spin, but are preferably deposited as individual fibers to the Build fiber mat precursor. Preference is given to staple fibers, wherein fibers in the region of a length of 3 to 25 mm are preferred and fiber denier numbers in the range 0.5 to 6 denier per filament (dpf). In a preferred embodiment the fibers are bicomponent staple fibers of PET and PPT in one Concentration ratio of from 70:30 to 30:70 and preferably from 60:40 to 40:60.

In a more preferred embodiment For example, the fibers used in the invention are uncrimped PET / PPT bicomponent staple fibers with a latent curling contraction of at least 40% and preferably 70 to 80%. Both PET and PPT are crystallizable polymers, but PPT has a higher crystallization rate as PET shows.

The in the present invention, preferred PET / PPT fibers leave by producing a melt stream of PET with an intrinsic viscosity (I.V.) from 0.4 to 0.8 and preferably 0.5 to 0.6 with a melt stream of PPT with an I.V. of 0.8 to 1.5 and preferably 0.9 to 1.0 are combined and the combined streams are fed to a multi-hole spinneret, from where it extrudes at a temperature of 260 ° to 285 ° C and preferably 265 ° to 270 ° C become. The extrudate is taken up and quenched and then wound up without a step of sticking. The spinning speed ranges from 1,900 to 3,500 m / min, with 2,000 to 3,000 m / min. are preferred. After spinning, the yarns are going to be cut on length from 3 to 25 mm, with lengths of from 20 to 25 mm being preferred are. The I.V. value is determined in p-chlorophenol to 25 ° C.

For the practitioner is taken for granted apply that the specific value of the spinning speed, which is the aimed at fiber properties, of the special Choice of the polymers used and depends on the technical Data of the spinning temperature, the fiber diameter and the type of Deterrence. For It will also be understood by those skilled in the art that the PET / PPT fiber suitable Range of spinning speed is different from the range of spinning speed will distinguish that for other compositions is suitable. For example, it is stated have been that for PET / PBT fibers the working range is about 1,700 to 3,200 m / min. is, being 1,800 to 3,000 m / min. preferred are; and in PPT / PBT fibers the working range 600 to 2,000 m / min. is, being 800 to 1,600 m / min. are preferred.

The staple fiber yarns produced in this way are then placed in Water with the help of a surfactant with a solids content in the range from 0.05 g / l to 1 g / l, and preferably from 0.25 g / l to 0.75 g / l. The dispersion is agitated without causing turbulence to obtain a homogeneous and well-separated mixture of fibers. The fiber dispersion is then deposited on a porous substrate and the excess water drained off and the resultant mat of fibers at one Temperature below 70 ° C and preferably about 40 ° C dried. The drying is preferably achieved during the aspiration of the surface.

Other means and media for dispersing the fibers can be used. The fibers can be dispersed using liquids other than water as long as the liquids are substantially inert. However, the fibers can also be dispersed in gaseous media, such as air, or in supercritical CO ₂ . However, the simplest method is that of dispersion with water using methods similar to those of the well-known papermaking method and thus preferred.

In an alternative embodiment of the present invention, the fibers are in the form of latent crimp multifilament continuous yarns. When using the continuous filaments, there must be a high degree of filament separation to produce the planar array or the fiber mat precursor suitable for the process of the present invention. One way to achieve this filament separation is to apply an electrostatic charge to the yarn bundle. The moving multifilament yarn bundle is electrostatically charged to a sufficient potential to separate each filament from adjacent filaments, after which the filaments separated in this manner are picked up as a random nonwoven web. The preferred yarn has a twist count or crimp of zero to provide maximum separation of the filaments. A minimum charge for charging is 30,000 electrostatic units (it E.). Charging is achieved while the filaments are under a sufficient tension so that they do not separate until such tension is released, ie, after they have been pressed against the receiving surface the Planar area is to be formed, after which they immediately separate from each other. The filaments can be charged by means of a corona discharge, by means of a triboelectric contact, by field charging or by other suitable methods. In one embodiment, freshly formed organic synthetic filaments produced according to the process of invention while still above their solidification temperature are charged by passing them through a high intensity electric field. A suitable apparatus and detailed procedures for electrically charging yarn bundles which are suitable for the practice of the present invention have been disclosed in U.S. Patent No. 5,376,874 US Patent No. 3338992 described. The filaments constituting the yarns thus treated are laid down to form an overlapping pattern to produce a planar region or a fiber mat precursor in which the filaments are predominantly oriented in the plane thereof.

The Thus produced planar array of continuous fibers then in a continuous or batchwise continuous Form transferred to a heat zone, where the latent ripples is developed and produces the nonwoven fabric of the present invention becomes. Although numerous methods for achieving heating up are known in the art, necessarily any method that for the Practice of the present invention is suitable, a limitation of Expansion in a direction perpendicular to the plane of the precursor tissue have as a consequence. One such method will be such batch type methods lock in, such as a stationary one heated zone between two plates, or such continuous Processing methods, such as calendering, or heated Conveyor belts. The Method with which the desired ripple is realized is not crucial as long as they are the prerequisite Fulfills, that while at least part of the heating the nonwoven structure itself in a restrictive way Contact with the restrictive ones surfaces located.

The Heating to develop the latent crimp of the fibers in the so Nonwoven fabric structure can be prepared by using a variety be achieved by methods such as those in the field of experience of a One of ordinary skill in the art. In the practice of Invention has been found to give satisfactory results by heating: (i) in hot air, such as in a hot air oven with forced air at a temperature above 80 ° C and preferred around 120 ° C or (ii) in water at a temperature of about 95 ° C. In the typical practice of the method of the invention is development the ripple within a few seconds of the specified thermal exposure. hot air is the preferred medium for heating when the distance between the restricting surfaces approximately 2 mm. In the practice of the method according to the invention it was found that heating the samples with hot water, which are thicker than about 2 mm, often leading to a sample breakage.

In a further embodiment It is an object of the present invention to provide entangled Nonwovens with high tenacity and controlled properties in the range of high stretch / lower Flexural rigidity up to high flexural strength / low stretch. This is accomplished (i) using high latent fibers ripple and (ii) limiting Expansion of the thickness of the textile fabric during the thermally induced area shrinkage according to the method of the invention, as described herein. The area shrinkage during the crimp is an indicator of the measure of Crimp development.

The nonwoven fabric of the invention has particularly desirable toughness properties defined as the Young's starting modulus product and its elongation at break. When a nonwoven fabric is made according to a preferred embodiment of the process of the present invention, a fabric is produced which exhibits Young's modulus values in the range of 1.2 to 12 MPa and an elongation at break of up to 150%. Preferred embodiments of the nonwoven fabric according to the invention provide combinations of elongation at break and tensile modulus in the range from about 30% or 6 MPa to 100% or 1.8 MPa in textile planar fabrics with bulk densities of 0.20 to 0.28 g / cm ³ .

The nonwoven fabric of the present invention comprises a plurality of entangled, spirally crimped side-by-side bicomponent fibers having a first crystallizable polyester component and a second crystallizable polyester component, the first crystallizable polyester component exhibiting a slower rate of crystallization than the second crystallizable polyester component, and the first crystallizable polyester component Fibers are characterized by a denier in the range of 0.5 to 6 dpf and wherein the fibers exhibit at least 19.7 crimps per cm (50 crimps per inch) with a curling radius of curvature of 0.2 mm or less, and wherein the Fibers are predominantly entangled with each other and further wherein the fibers are predominantly oriented in a well-defined plane of the nonwoven fabric, characterized by a bulk density of 0.2 to 0.4 g / cm ³ .

The density of the nonwoven fabric of the invention is determined by cutting out a sample of known area, determining its thickness and weight, and calculating the density according to the formula: (Density) = weight (g) / (area (cm 2 ) × thickness (cm))

Of the Nonwoven fabric of the present invention is easy to compress and offers many spaces between the fibers. To get an accurate measurement of the thickness to make an accurate determination of the density is therefore problematic. Usually, the thickness of objects, such as films and textile fabrics, determined in the art using a contact thickness gauge, wherein the sample to be measured between a fixed anvil and a vertically movable foot is placed on a certain device is attached to the thickness display. If the vertically sliding foot one too narrow cross-section, it can between adjacent fibers slip, resulting in a faulty low thickness reading becomes. When the vertically movable foot is on the area to be measured one too big Pressure, This can lead to a compression of the fabric and again come to a faulty low thickness reading.

Around these pitfalls To circumvent the thickness measurement using a thickness gauge with a vertically movable foot with a flat sample contact surface with circular cross section with a diameter of at least 0.5 cm executed be applied and a total force of not more than 95 g. The measurement accuracy should be at least ± 0.0005 cm. Although Any instrument that satisfies these restrictions, to determine the thickness the sample according to the invention suitable, several commercially available instruments are available, which are sufficient. One of these instruments for the determination the thickness according to the invention has been found to be suitable, the "Model PT223 Federal (Providence, RI) C2I Comparator ", that with a contact foot Model PT223 attached on a stand Model 35B-8-R-1 is provided. The thickness measurement should be one Mean value of at least three readings, which at different Points were taken on the sample.

The Weight is on a laboratory balance with a precision of at least 0.0001 g determines.

The for the Use in the nonwoven fabric according to the invention suitable bicomponent fibers are preferably side-by-side bicomponent fibers, the selected are on the group consisting of PET / PPT, PET / PBT and PPT / PBT fibers. In the aforementioned group, the first crystallizable polyester component is stated first and the second crystallizable component as the second stated. In other words, the polymers are with the slower crystallizing polymer listed first. At the Most preferred is the bicomponent fiber of a side-by-side bicomponent fiber at the PET / PPT.

The preferred for use in the nonwoven fabric of the invention PET / PPT fibers can be made by adding a melt stream PET with an intrinsic viscosity (I.V.) of 0.5 to 1.2 and preferably 0.7 to 0.9 with a melt stream from PPT with an I.V. of from 0.8 dl / g to 1.5 dl / g and preferred 0.9 to 1 combined and the combined streams are fed to a multi-hole spinneret, from where they are at the respective hole of single bicomponent strand at a temperature of 265 ° to 285 ° C and preferably extruded from 265 ° to 270 ° C becomes. The extrudate is taken up and quenched and then without a step of stretching wound up. The winding speed, which is synonymous in this case with the spinning speed lies in the range of 2,000 to 3,500 m / min, whereby 2,500 to 3,000 m / min. are preferred. After spinning, the yarns are going to be cut on length from 3 to 25 mm with preferred lengths of 25 mm. The I. V. becomes at 25 ° C determined in p-chlorophenol.

The in this way produced preferred fibers are then after processed and lead to the method already described herein the nonwoven fabric according to the invention.

The unusually high density and high recovery of the nonwoven webs of the present invention make them applicable in fields such as fine particle filtration and in protective application. Nonwovens are ideal candidates for applications for the removal of technical dusts, which allows their random arrangement of fibers rapid distribution of the carrier phase into the individual streams. The vast majority of nonwovens is needled and usually known as "needle felts" with densities of about 0.2 g / cm ^3. At the same density, the fabrics of the present invention are expected to possess superior filtration performance, as they easily result in a three-dimensional, random array of fibers. The latter greatly facilitates the construction of "dust bridges" that are crucial to rapidly reduce the penetration of dust down to extremely low levels.

In another embodiment, can be adapted for use in the present invention, suitable bicomponent fibers preferably combined with polyamide fibers during the deposition of the Faserniattenptakursors such as Nomex ^® and Kevlar ^® fibers, which are available from the DuPont Company, the strength, heat resistance and puncture resistance of the reinforce resulting textile fabric. In this embodiment, the polyamide staple fibers, which generally do not exhibit thermal shrinkage, are blended with the bicomponent fibers useful in the practice of the invention to produce the fiber mat tip cursor. During crimp development according to the method of the present invention, the polyamide fiber undergoes twisting and entanglement with the crimped bicomponent fibers by forming a particularly reinforced network of entangled fibers by tying the polyamide fibers to the nonwoven fabric. This intimate bond can be achieved without the use of binders commonly used in the generation of blends involving polyamides.

In the nonwoven fabric according to the invention can be effortlessly surface modifiers and incorporating additives to, for example, antimicrobial and impart flame-retardant properties. Other polymeric fibers, the one latent rippling or no latent ripples show, can also effortlessly through Compounding the bicomponent fiber in the practice of the invention work in and especially by combining the fibers in the step the aqueous slurry the preferred embodiment the invention. To improve flame retardancy and abrasion resistance For example, the addition of short polyaramid fibers may be considered to be pulled.

The The present invention will become apparent from the following specific embodiments described in more detail, but without being limited thereby.

EXAMPLES

The Fiber used in the following examples was a side-by-side bicomponent yarn with a relationship of PET (Crystar 4415, IV = 0.54 +/- 0.02) and PPT (CIDU, IV = 1.04 + 1 - 0.03) from 50:50.

The polymers were spun from the melt through a 34-hole spinneret at 265-270 ° C according to standard procedures in the art using an extrusion block and a standard spinneret stack as taught in the art for side-by-side production. Side bicomponent fibers as described in Evans et al. in the US Patent No. 3671379 well known.

The Extrudate was cooled, by passing through a cross-flow quench zone of a length of 182.9 cm (72 inches) with a stream of cooling air at room temperature, at right angles to the yarn path at approximately 10 m / min. moving. This was then without any stretching step in the special Example speed wound up. The resulting Yarn was smooth, d. H. it showed no visible ripples.

To The spinning was again the yarn in lengths of 90 m each on a small motorized reel device with a diameter wound up by 11 cm. Each reel was then closed with scissors Short fiber flakes cut the length specified in the specific example. It became a solution of 5 grams of F-98 Prill, a surfactant available from BASF Corp., Mt. Olive, NJ, in 2 liters of water in the container a "Williams Standard Pulp Testing Apparatus "with Dimensions of 28 cm × 28 cm × 28 cm cast. additionally Cold water was added to fill the container, after which it was split slightly Add 6g of flakes to the pulp apparatus using a spatula were and the watery slurry for about 30 seconds using a hand follower, the off a wide steel plate with holes it consisted. Special attention was paid to to prevent turbulence, which inevitably leads to flocculation leads. The water was then drained off, creating a fiber mat the porous one Cloth at the bottom of the container was filed.

The blanket and the fiber mat were then laid down on a sheet dryer also manufactured by Williams Apparatus, Watertown, NY. The in 1 The sheet dryer shown consisted of a porous metal drum 1 , half its circumference or less, the cloth and fiber mat 2 were released. To place the mat firmly, became a layer of lattice linen 3 that at the one end 4 was attached to the surface of the drum over the cloth and the fiber mat 2 placed and with by turning a knob 5 tightened, to which the other end of the layer of grid was attached. By Dre By pressing the button manually to the desired degree of density, the pressure exerted on the fabric and the fiber mat by the position of the grid lines can be varied over a wide range, albeit somewhat subjectively.

The Mat was at 35 ° up 40 ° C dried. The drying was carried out under light pressure, which was achieved by tightening the covering the layer by about two turns of the button was obtained. After a drying time of one hour was the mat taken and samples in a square of 7.62 cm × 7.62 cm (3 inches x 3 Inch). Each sample was then separated between two with Teflon-coated aluminum plates of 16 cm × 21 cm × 0.7 cm were inserted, the one Each weighing 554 g. The distance between the plates was achieved by inserting washers of varying thickness regulated from 0.25 to 4 mm. The composite (2 plates + sample + Washers) was then heated by means of hot air at 120 ° C for about 30 Heated for a few minutes.

The entire mechanical test was done using a bench top "Instron Tensile Tester", Model 1123. The Machine was supplemented with the MTS Ranew Package, which is the MTS Testworks software version 4.0 contained.

The crimp (CC) of the method according to the invention Gaens used was rated as follows: It was one piece 10.2 cm (4 inches) of yarn heated in hot air for 30 minutes at 120 ° C. The piece was then hung from its midpoint on a hook, whereby a loop was formed and its two ends were taped shut. Let L1.5 be the yarn length under a load of 1.5 mg / d attached to its glued ends, and with L100 that under a load of 100 mg / d, it is calculated the curling contraction as CC (%) = [(L100 - L1.5) / L100] × 100. Um To obtain the result, the mean of three samples was taken.

to Determination of the number of ripples per centimeter (crimping per 0.39 inch) a separate yarn sample was made as in the test crimp contraction heated. This was then sandwiched between two glass plates placed and using a stereoscope with skylight at an enlargement of -16fold examined. The number of ripples per centimeter was obtained by placing the number of peaks on one side of the fiber axis over a Section with an end-to-end distance equal to one centimeter (0.39 Inch).

The Density was determined by measuring the thickness of a square-shaped sample of 7.62 cm × 7.62 cm (3 inches x 3 Inch) using a "Federal C21 Comparator" gauge, on a stand (Model 35B-8-R-1) was constructed. The comparator had a flat Contact point, model PT223, which exerted a total force of 93 ± 2 g, and had a foot diameter 0.46 cm (0.18 inch). The thickness was an average of five determinations in different places on the sample.

The Weight of the tissue sample was measured using a Mettler8200 balance determined with an accuracy of 0.0001 g.

In front the heat treatment has a typical wet-laid leaf made from 0.64 cm (1/4 inch) flakes was, thicknesses of 0.28 ± 0.02 mm.

Area shrinkage was measured for the entire sample using the relationship 100 * (A _before -A _after ) / (A _before ) where A _before and A _after the area of the square sample before and after shrinkage.

EXAMPLE 1:

In accordance with the procedures described hereinabove, a 34 filament 50/50 PET / PPT bicomponent yarn of 5.9 denier per filament was applied at a speed of 3030 m / min. spun. The yarn bundle shows a tensile strength of 1.6 g / denier. The yarn thus prepared was cut into 2.54 cm (1 inch) flakes with scissors and processed in the Williams Standard Pulp Testing Apparatus using the hot air heating method described hereinabove. The resulting crimped yarn had the following properties: crimp contraction CC = 74%, number of crimps per centimeter 22.8 (crimps per inch 58) with a mean radius of curvature of 0.13 mm. The properties of the fabric for different thicknesses of the shims are shown in Table I. Each value was an average over two samples. The product of modulus and elongation (referred to as toughness) had a constant value of about 2. Table I Washers (m / m) Area shrinkage (%) Surface density (g / m ² ) Modulus density (g / d) Elongation at max. Load (%) Modulus elongation (g / d ×%) Density (g / cm ³ ) 0.25 44 226 0,055 35 1.9 0.28 0.50 58 179 0.045 50 2.2 0.24 1 67 350 0,035 70 2.4 0.23 2 79 533 0,022 88 1.9 0.23 4 84 504 0,014 95 1.4 0.20

EXAMPLE 2

The materials and procedures of Example 1 were repeated except that prior to dispersion in the "Williams Standard Pulp Apparatus" the 2.54 cm (1 inch) flakes in a 1% (w / w) solution of polyethylene oxide (Mw = 900,000) were completely wetted in water. The results are shown in Table II. Table II Washers (m / m) Area shrinkage (%) Surface density (g / m ² ) Modulus density (g / d) Elongation at max. Load (%) Modulus elongation (g / d ×%) Density (g / cm ³ ) 0.25 48 169 0.053 34 1.8 0.26 0.50 47 180 0.048 44 2.0 0.24 1 72 270 0,029 58 1.7 0.24 2 79 422 0,017 93 1.8 0.22 4 88 552 0,012 120 1.5 0.22

EXAMPLE 3

The materials and procedures of Example 1 were repeated except that the fiber was cut into 0.64 cm (¼ inch) flakes. The results are shown in Table III. Table III Washers (m / m) Area shrinkage (%) Surface density (g / m ² ) Modulus density (g / d) Elongation at max. Load (%) Modulus elongation (g / d ×%) Density (g / cm ³ ) 0.25 49 144 0,038 28 1.1 0.24 0.50 67 204 0.024 48 1.2 0.24 1 75 286 0,022 64 1.4 0.24 2 81 348 0,010 90 0.9 0.21 4 86 546 0,013 82 1.1 0.23

COMPARATIVE EXAMPLE 1

The methods and materials of Example 3 were repeated except that the yarn at 1850 m / min. spun and resulted in a 4.7 denier per filament yarn having a tensile strength of about 1.17 g / d. In the development of its latent crimping using the methods set forth above, the yarn had the following properties: crimp contraction CC = 0.42, number of crimps per centimeter 6.7 (number of crimps per inch 17) at a mean radius of curvature of about 1.1 mm. The results are shown in Table N. The flake had a length of 0.64 cm in this example. Table IV Washers (m / m) Area shrinkage (%) Surface density (g / m ² ) Modulus density (g / d) Elongation at max. Load (%) Modulus elongation (g / d ×%) Density (g / cm ³ ) 0.25 0 68 0.10 3 0.3 0.18 0.50 0 70 0.09 4 0.4 0.19 1 8th 71 0.02 7 0.2 0.19 2 28 92 0,007 19 0.2 0.20 4 49 145 0,004 40 0.2 0.19

COMPARATIVE EXAMPLE 2

The materials and procedures of Example 1 were repeated except that the floc length was 51 mm. The results are shown in Table V. Table V Washers (m / m) Area shrinkage (%) Surface density (g / m ² ) Modulus density (g / d) Elongation at max. Load (%) Modulus elongation (g / d ×%) 0.50 59 171 0.045 55 2.5 1 76 260 0,017 85 1.5 2 82 385 0,012 139 1.7 4 87 692 0,010 152 1.5

COMPARATIVE EXAMPLE 3

This Example illustrates that at drying temperatures above from 60 ° C restricted to shrinking Fibers of a hot curing which resulted in latent crimping.

The materials and procedures of Example 3 were repeated with drying at different temperatures as indicated in Table VI. However, unlike in Example 3, the canvas layer which covered the fiber mat during drying was strongly attracted to exert pressure on the fiber mat and limit the mobility of the fibers, thereby preventing shrinkage. The results are for a yarn running at 3,030 m / min. was spun into 0.64 cm (¼ inch) flakes and then heat treated in hot air using 2 mm washers. Table VI Drying temperature (° C) Area shrinkage (%) Surface density (g / m ² ) Module (g / d) Elongation at max. Load (%) Modulus × elongation (g / d,%) 23 79 364 0,013 84 1.1 40 82 432 0,013 98 1.3 60 73 290 0,017 74 1.3 80 0 64 0.009 41 0.4

COMPARATIVE EXAMPLE 4

The materials and procedures of Example 3 were repeated except that the step of curling development in water of 95 ° C was carried out. The results are shown in Table VII. The specimens on shims with a large thickness of> 1 mm broke in the water. Table VII Washers (m / m) Area shrinkage (%) Surface density (g / m ² ) Modulus density (g / d) Elongation at max. Load (%) Modulus elongation (g / d ×%) Density (g / cm ³ ) 0.25 28 94 0.027 24 0.6 0.27 0.50 40 125 0.056 22 1.2 0.28 1 75 302 0.024 31 0.7 0.33 2 - 4 -

COMPARATIVE EXAMPLE 5

The same as in Comparative Example 4, but for a at 1850 m / min. spun yarn. The results are shown in Table VIII. Table VIII Washers (m / m) Area shrinkage (%) Surface density (g / m ² ) Modulus density (g / d) Elongation at max. Load (%) Modulus elongation (g / d ×%) Density (g / cm ³ ) 0.25 0 64 0.23 3 0.7 0.20 0.50 0 73 0,038 5 0.2 0.23 1 11 76 0,029 9 0.3 0.20 2 48 132 0.011 23 0.3 0.24 4 76 323 0.011 37 0.4 0.20

Claims (20)

A nonwoven web comprising a plurality of entangled, spirally-crimped asymmetric bicomponent fibers comprising a first crystallizable polyester component and a second crystallizable polyester component, the first crystallizable polyester component exhibiting a slower rate of crystallization than the second crystallizable polyester component and wherein the fibers are characterized by a denier region from 0.5 to 6 denier and wherein the fibers exhibit at least 19.7 crimps per centimeter (50 crimps per inch) with a curling radius of curvature of 0.2 mm or less, and wherein the fibers are predominantly entangled with each other and further wherein the fibers are predominantly oriented in a well-defined plane and the nonwoven fabric is characterized by a bulk density of 0.2 to 0.4 g / cm ³ . The nonwoven fabric of claim 1, wherein the bicomponent fibers Side-by-side bicomponent fibers. The nonwoven fabric of claim 1, wherein the first crystallizable Polyester component is poly (ethylene terephthalate) and the second crystallizable polyester component poly (propylene terephthalate) is. The nonwoven fabric of claim 1, wherein the first crystallizable Polyester component is poly (propylene terephthalate) and the second crystallizable polyester component poly (butylene terephthalate) is. The nonwoven fabric of claim 1, wherein the first crystallizable Polyester component is poly (ethylene terephthalate) and the second crystallizable polyester component poly (butylene terephthalate) is. Nonwoven fabric according to claim 1, wherein the bicomponent fibers predominantly Staple fibers are. The nonwoven fabric of claim 6, wherein the first crystallizable Polyester is poly (ethylene terephthalate) and the second is crystallizable Polyester poly (propylene terephthalate) at a concentration ratio in Range is from 70:30 to 30:70. Nonwoven fabric according to claim 7, wherein the concentration ratio in Range from 60:40 to 40:60. The nonwoven fabric of claim 1, wherein the bicomponent fibers are endless. The nonwoven fabric of claim 1, further characterized through a Young's initial modulus of 1.2 to 12 MPa and through an elongation at break up to 150%. A nonwoven fabric comprising a plurality of entangled, spirally crimped side-by-side bicomponent staple fibers in the range of 0.5 to 6 denier and an uncrimped length in the range of 20 to 25 mm comprising polyethylene terephthalate and polypropylene terephthalate at a concentration ratio in the range of 60:40 to 40:60, wherein the fibers exhibit at least 19.7 crimps per centimeter (50 crimps per inch) with a curling radius of curvature of 0.2 mm or less, and wherein the fibers are predominantly entangled with each other and wherein the fibers are predominantly in one well-defined plane of the nonwoven fabric, characterized by a bulk density of 0.2 to 0.4 g / cm ³ , a Young's initial modulus of 1.2 to 12 MPa and an elongation at break of up to 150%. A method of producing a nonwoven fabric which Method of depositing a plurality of asymmetric bicomponent fibers with a latent rippling in a planar area of overlapping Fibers, the fibers predominantly in its plane are oriented, with the planar region between two limiting surfaces is arranged; Heating the Planar area to development at least part of the latent crimp provided that at least during part of the heating the nonwoven structure is in restrictive contact with the limiting ones surfaces located. The method of claim 12, wherein the planar region in the form of a fiber mat preform. The method of claim 12, wherein the bicomponent fibers Side-by-side bicomponent fibers. The method of claim 12, wherein the bicomponent fibers consist essentially of polyester. The method of claim 12, wherein the first crystallizable Polyester component is poly (ethylene terephthalate) and the second crystallizable polyester component poly (propylene terephthalate) is. The method of claim 12, wherein the first crystallizable Polyester component is poly (propylene terephthalate) and the second crystallizable polyester component poly (butylene terephthalate) is. The method of claim 12, wherein the first crystallizable Polyester component is poly (ethylene terephthalate) and the second crystallizable polyester component poly (butylene terephthalate) is. The method of claim 12, further comprising Step of producing the fiber mat preform from an aqueous slurry of flakes with a mean length of 3 to 25 millimeters. A method of producing a nonwoven fabric which Method of producing a fibrous mat preform from an aqueous slurry of uncurled Side-by-side bicomponent staple fibers with a latent curling contraction at 70 to 80%, one length from 20 to 25 millimeters and the laying of the fiber mat preform between two restrictive ones Surfaces; Heating the planar area to develop at least one Part of the latent ripples provided that during at least a part of heating the fiber mat preform in a restrictive manner Contact with the restrictive ones surfaces wherein the bicomponent fibers are polyethylene terephthalate and polypropylene terephthalate in a corresponding concentration ratio in Range from 60:40 to 40:60.