KR101065094B1 - High stretch recovery non-woven fabric and process for preparing - Google Patents

Abstract

The present invention relates to a process for making such nonwovens by using novel nonwovens and potentially crimped fibers characterized by having a high rate of elongation recovery.

Elongation recovery, potential crimp, nonwovens, bicomponent fibers, restraint surface

Description

Nonwoven fabric with high elongation recovery rate and manufacturing method thereof {HIGH STRETCH RECOVERY NON-WOVEN FABRIC AND PROCESS FOR PREPARING}

The present invention relates to a new nonwoven fabric characterized by having a high rate of elongation recovery, and a process for making such nonwoven fabrics by using potential crimped fibers.

Nonwoven fabrics made from thermoplastic synthetic fibers are known in the art and are widely used commercially as DuPont Company's trademarks such as Tyvek® and Sontara®.

In nonwoven fabrics, bulky fabric-like products having a high elongation recovery and at the same time high elongation have been sought. Such nonwovens are collectively known as "stretch non-wovens". Numerous methods have been implemented for making extensible nonwovens.

One method of making an extensible nonwoven is to use crimped staple fibers, in which entanglement of the crimped fibers provides the flocculation and recovery needed for the extensible nonwoven. In some cases in the art, crimped fibers are mated and interlaced using air or water sprayers. In some cases in the art, straight or nearly straight fibers with potential crimps are first made into a mat and then heated to express potential crimps, thereby creating a "self-entangled" structure. Extensible nonwovens in the art, however, do not have toughness defined as the product of tensile modulus and ultimate elongation, and density useful in many textile and industrial applications. It is the toughness of nonwovens that determines “elongation” which means stretchable amount and resilience. Stretchable nonwovens in the art are limited only to fabrics of low density, that is to say in the art, high loft, very low stretch.

Japanese Patent Application Laid-Open No. 11-158733 to Aranaga et al. Discloses a wet-lay process for producing a nonwoven fabric from bicomponent fibers of polyethylene terephthalate / polypropylene terephthalate having potential crimp. The resulting nonwovens are said to have a high recovery rate. The wet-integrated process involves hydroentangling the fibers to provide sufficient entanglement before developing the crimps. The nonwoven fabric thus produced has a basis weight of 30 g / m 2 in the case of a 0.3 mm thick nonwoven fabric. In Aranagar's literature and other documents, crimped fibers with high recovery rates have the potential to produce high quality nonwovens. However, as is clearly recognized in Aranaga's literature, fibers with high traction tend to crimp independently, resulting in increased volume and reduced entanglement, which is a problem. This is often associated with nonwoven breakage during shrinkage. The result is a bulky nonwoven that is typically suitable for non-load applications, where the full potential of fibers with high recovery rates is not realized.

Furukawa, US Pat. No. 4,469,540, discloses bulky nonwovens having a bulk density of less than 0.020 g / cm 3, formed from crimped polyolefin bicomponent staple fibers. Numbers of crimps in excess of 4.7 per centimeter (12 per inch) interfere with web formation because these crimp numbers make the web density too high. The structure according to Furukawa is "melt-bonded" by thermal bonding, and said melt-bonding, rather than fiber entanglement, is the main mechanism by which these structures are fixed together.

WO 00/18995 to Stokes et al. Discloses a method of forming a bulky nonwoven fabric having compressive resistance from crimped bicomponent polyolefin fibers and crosslinking to maintain elasticity.

EP 0 391 260 B1 of Terakawa et al. Air-entangles a bundle of yarns with potential crimps, heats them to the temperature at which crimps develop, and heats them to a temperature that causes bonding at the junction, Disclosed is a method of making a nonwoven fabric from continuous bicomponent polyolefin fibers. The nonwovens according to Terrakawa have a density of less than 0.030 g / cm 3.

US Pat. No. 5,540,976 to Shawver et al. Discloses an extensible nonwoven fabric made from a radiobond material laminated to an elastomeric inner layer sheet.

Pike et al. US Pat. No. 5,418,045 discloses a process for making nonwoven webs from continuous multicomponent thermoplastic fibers, in particular polyolefins, having potential crimps, which are crimped to varying degrees in air, prior to forming a thermally bonded nonwoven.

Summary of the Invention

The present invention provides a nonwoven fabric comprising a plurality of entangled spiral crimped asymmetric bicomponent fibers comprising a first crystallizable polyester component and a second crystallizable polyester component, wherein the first crystallizable polyester component comprises: Exhibit a lower crystallization rate than the second crystallizable polyester component, the fiber having a denier range of 0.5 to 6 denier, wherein the fiber has a crimp number per centimeter of at least 19.7 (number of crimps per 50 or more) And a crimp radius of curvature of 0.2 mm or less, the fibers being entangled with each other, further the fibers are oriented mainly in a well-defined plane, and the nonwoven fabric has a bulk density of 0.2 to 0.4 g / cm 3. do.

The present invention places a plurality of asymmetric bicomponent fibers with potential crimp in a planar arrangement of overlapping fibers, such that the fibers are oriented primarily in their planes, and the planar arrangement is disposed between two constraining surfaces. To; A method of making a nonwoven fabric is further provided comprising heating the planar array such that at least a portion of the potential crimp is expressed, while forcing the nonwoven structure into contact with the restraining surface during at least a portion of the heating.

1 is a layout view of the wet fibrous mat precursor and cloth support on a dry drum of the Williams Pulp Testing Apparatus.

Methods of making nonwoven fabrics are known in the art which produce a planar arrangement of bicomponent fibers with potential crimps, typically a fibrous mat and then express the crimps by heating to entangle the fibers to create a stable nonwoven structure. It is. During the crimp-expression step, the fibrous mat or other structure contracts in a plane and expands in a direction perpendicular to the plane. As a result, nonwovens in the art generally have very low bulk densities, well below 0.1 g / cm 3. As a result, it has limited utility in many fabric applications requiring high toughness or high elongation recovery.

The present invention is based on the discovery that during the crimp development process, by carefully controlling the expansion of the nonwoven in a direction perpendicular to the plane of the nonwoven, it can promote entanglement formation of fibers with high crimp and high recovery rates. In processes in the art, crimp expression typically results in widespread contraction in the plane and expansion in a direction perpendicular to the plane.

In the process of the present invention, in the first step, a plurality of asymmetric bicomponent fibers with potential crimps are arranged to provide a planar arrangement of the fibers, the fibers being oriented primarily in their plane, with the majority of the fibers being one In contact with each other, the fibers are different. In a preferred embodiment said planar arrangement is referred to herein as a "fibrous mat preform", which refers to the nonwoven structure before being subjected to the crimp expression step, which is the second step of the process of the invention. The crimping expression step is performed by heating the planar array so that the crimp is expressed, while placing the planar array between two constraint surfaces oriented at least approximately parallel to the plane of the planar array. During at least a portion of the crimp expression step, the spacing between the two restraining surfaces is adjusted such that expansion of the planar arrangement in a direction perpendicular to the planar surface is suppressed by simultaneous contact with the two restraining surfaces. This contact during the expansion step provides a compressive force on the contracting arrangement. The nonwoven fabrics thus produced exhibit higher density and stronger physical properties than nonwoven fabrics made from comparable starting materials produced without inhibiting expansion in a direction perpendicular to the planar surface.

Bicomponent fibers suitable for the process of the present invention are fibers comprising two polymers, preferably belonging to the same group, which exist as two adjacent phases adjacent to each other that exhibit different shrinkage rates to allow for the expression of spiral crimps upon shrinkage. . The phases can be arranged in side-by-side arrangement or asymmetrical seed-core arrangement. Side by side arrangement is preferred. Suitable bicomponent fibers include, but are not limited to, bicomponent polyesters, bicomponent polyamides, and bicomponent polyolefins. Polyester is preferred. Copolymers of polymers belonging to this broad class are also included. Preferred bicomponent fibers among the polyesters include polyethylene terephthalate (PET) / polypropylene terephthalate (PPT), PET / polybutylene terephthalate (PBT), and PPT / PBT, with PET / PPT being preferred.

Fibers, often referred to as biconstituents (including polymers belonging to different groups, such as polyamides and polyesters), are also included in the term "bicomponent". However, bicomponent fibers are less preferred.

For the purposes of the present invention, a fiber having a potential crimp, typically, when at least one of the components is heated to a temperature higher than its glass transition temperature, can exploit the difference in shrinkage behavior of the two components to develop additional crimps. It is a fiber with a unique ability. Potential crimped fibers may exhibit some crimp or no crimp at all. In the practice of the present invention, the potential crimped fibers are preferably flat without crimping.

The inventors of the present invention restrain the expansion of the nonwoven fabric in a direction perpendicular to the plane, for example, by performing a crimp expression step using a nonwoven fabric disposed between two metal plates parallel to the plane of the fibrous mat prestructure. When crimped expression is performed under such conditions, it is found that the nonwoven fabric becomes significantly dense and the individual fibers are more entangled. As a result, a nonwoven fabric having a denser, stronger and more improved elongation recovery is obtained, compared to nonwoven fabrics produced by the prior art methods using the same fibrous mat prestructure.

The degree of densification and achievable properties depend not only on the crimp contraction of certain types of fibers used in the present invention, but also on the starting bulk density of the planar arrangement, the degree of fiber overlap with each other, and the separation gap between restraining surfaces. Will depend. If other conditions are the same, both higher crimp shrinkage, higher overlap between fibers, higher starting bulk density, and narrower spacing between restraining surfaces (to the point where the fibers no longer slip and the crimp is significantly suppressed) Is associated with higher nonwoven density, higher toughness and higher elongation recovery.

The advantages of the process of the present invention are so broad that it can be applied to the production of nonwovens of almost any composition, in which bicomponent fibers with potential crimps are used for the planar arrangement of the overlapping fibers.

The fibers used in the present invention may be in the form of continuous or long fibers or may be staple fibers. The continuous fibers can be spun in the form of multifilament yarns but are preferably deposited as individual fibers to form fibrous mat precursors. Preferred are staple fibers having a length of 3 to 25 mm and a fiber denier of 0.5 to 6 denier / filament (dpf). In a preferred embodiment, the fibers are staple bicomponent fibers of PET and PPT, each having a ratio of 70:30 to 30:70, preferably 60:40 to 40:60.

In a more preferred embodiment, the fibers used in the present invention are non-crimped staple PET / PPT bicomponent fibers having a potential crimp shrinkage of at least 40%, preferably 70 to 80%. Both PET and PPT are crystallizable polymers. However, PPT shows higher crystallization rates than PET.

Combining a melt stream of PET having an intrinsic viscosity (IV) of 0.4 to 0.8, preferably 0.5 to 0.6, and a melt stream of PPT having an IV of 0.8 to 1.5, preferably 0.9 to 1.0, By feeding the porous spinneret and extruding it at a temperature of 260 to 285 ° C., preferably 265 to 270 ° C., preferred PET / PPT fibers can be produced for use in the present invention. The extrudate is recovered and quenched and then wound up without going through the stretching step. The spinning speed is 1900 to 3500 m / min, preferably 2000 to 3000 m / min. After spinning, the yarn is cut into 3 to 25 mm, preferably 20 to 25 mm. I.V. was determined in p-chlorophenol at 25 ° C.

Those skilled in the art will appreciate that the specific spinning rate values that provide the desired fiber properties will depend on the particular type of polymer used, the specific spinning temperature, the fiber diameter and the type of quench. Those skilled in the art will also appreciate that the spin rate range suitable for PET / PPT fibers differs from the spin rate range suitable for other compositions. For example, for PET / PBT fibers, the working range is about 1700 to 3200 m / min, preferably 1800 to 3000 m / min, while for PPT / PBT fibers, the working range is 600 to 2000 m / min. , Preferably 800 to 1600 m / min.

The staple fiber yarn thus prepared is dispersed in water to a solid content of 0.05 to 1 g / l, preferably 0.25 to 0.75 g / l, with the aid of a surfactant. The dispersion is stirred without causing disturbance to obtain a homogeneous, well-separated fiber mixture. The fiber dispersion is then deposited on the porous substrate, excess water is drained, and the resulting fiber mat is dried at a temperature below 70 ° C., preferably about 40 ° C. Preferably drying is carried out by blotting the surface with an absorbent body.

Other means and media for dispersing the fibers can be used. As long as the liquid is essentially inert, the fibers can be dispersed as a liquid other than water. Alternatively, the fibers can be dispersed in a gaseous medium, such as air, or in supercritical CO ₂ . However, water-dispersion methods using techniques similar to the well known papermaking methods are most convenient and preferred.

In another embodiment of the invention, the fibers are in the form of continuous multifilament yarns with potential crimps. When using such continuous filaments, a high degree of filament separation must be achieved in order to form planar arrays or fibrous mat precursors suitable for the process of the present invention. One way to achieve this filament separation is to impart an electrostatic charge to the bundle. The moving multifilament yarn bundles are electrostatically charged to a potential sufficient to separate each filament from adjacent filaments, and during this separation, the filaments are recovered as random nonwovens. Preferred yarns do not have flammable or crimped to achieve maximum filament separation. The minimum charge level is 30,000 electrostatic units (esu). During the charging, the filaments are under sufficient tension, and the filaments do not separate until this tension is released. In other words, only after the filaments are oriented towards the receiving surface on which the planar arrangement is formed, the filaments are immediately separated. The filaments may be charged by corona discharge, triboelectric contact, field charge or other suitable method. In one embodiment, the newly formed, synthetic organic filaments, which are produced according to the process of the present invention, still above the freezing point, are charged by passing them through a high intensity electric field. Apparatuses and detailed procedures suitable for imparting electrostatic charges to yarn bundles suitable for the practice of the present invention are described in US Pat. No. 3,338,992. The filaments constituting the yarn thus treated are integrated to form an overlap pattern to make a planar arrangement or fibrous mat precursor, wherein the filaments are mainly oriented in their plane.

The planar array of continuous fibers thus produced is then conveyed to a heating zone in a continuous or batch continuous manner, where potential crimps are expressed and the nonwoven fabric of the invention is produced. While many methods for providing heating are known in the art, any method suitable for practicing the present invention necessarily includes inhibiting expansion in a direction perpendicular to the precursor nonwoven plane. Such methods would include batch processes such as static heating zones between two plates, continuous processing methods such as calendering, or heated conveyors. During at least a portion of the heating, the method of developing the desired crimp is not critical, provided that the nonwoven structure is restrained in contact with the restraining surface.

Heat expression of the potential crimp of the fibers in the nonwoven structure thus produced can be carried out using a variety of methods well known to those of ordinary skill in the art. In the practice of the present invention, (i) at a temperature above 80 ° C., preferably at about 120 ° C., heating in hot air, such as in a hot air oven of forced convection flow mode, or (ii) at a temperature of about 95 ° C. It has been found that by heating in water, satisfactory results can be achieved. In a typical implementation of the process of the present invention, crimp expression occurs several seconds after the indicated heat exposure. If the distance between the restraining surfaces is greater than about 2 mm, hot air is the preferred heating medium. In the practice of the process of the present invention, it has been found that heating a sample whose thickness is greater than about 2 mm with hot water often causes the sample to break.

In a further embodiment, it is an object of the present invention to provide a tangled nonwoven with controlled properties and high toughness in the range of high elongation / low stiffness to high stiffness / low elongation. Such nonwovens are obtained by (i) using fibers with a high potential crimp and (ii) inhibiting the expansion of the nonwoven thickness during thermally induced area shrinkage according to the inventive process described herein. The area shrinkage rate during crimp expression is an indicator of the extent of crimp expression.

The nonwoven fabric of the present invention has a particularly desirable property of toughness, defined as the result of multiplying the initial Young's modulus by its ultimate elongation. When the nonwoven is produced according to a preferred embodiment of the process of the present invention, nonwovens are produced that exhibit an initial Young's modulus of 1.2 to 12 MPa and an ultimate elongation of 150% or less. Preferred embodiments of the nonwovens of the present invention provide a combination of ultimate elongation and tensile modulus of about 30% and 6 MPa, to 100% and 1.8 MPa, respectively, for nonwovens having a bulk density of 0.20 to 0.28 g / cm 3.

The nonwovens of the invention comprise bicomponent fibers in a side-by-side arrangement having a plurality of tangled spiral crimps, comprising a first crystallizable polyester component and a second crystallizable polyester component, wherein the first crystallizable polyester component comprises: Exhibit a lower crystallization rate than the second crystallizable polyester component, the fibers having a denier range of 0.5 to 6 dpf, wherein the fibers have a crimp number per centimeter of at least 19.7 (number of crimps per 50 or more) And a crimp radius of curvature of 0.2 mm or less, wherein the fibers are entangled with each other, further the fibers are oriented primarily within a well-defined plane, and the nonwoven fabric has a bulk density of 0.2 to 0.4 g / cm 3. do.

The density of the nonwoven fabric of the present invention is determined by cutting a specimen of known area, determining its thickness and weight, and calculating the density according to the following formula.

∂ (density) = weight (g) / (area (cm2) × thickness (cm))

The nonwoven fabric of the present invention is easy to compress, so that many gaps are formed between the fibers. Therefore, the question is whether the thickness can be measured accurately to accurately determine the density. Typically in the art, the thickness of objects such as films and fabrics is measured with a contact thickness meter, which measures the specimen to be measured between a vertically movable foot coupled to a fixed anvil and some means of indicating thickness. To put on. If the vertically movable foot has a too narrow cross sectional area, it slips between adjacent fibers, so that an incorrect small thickness can be read. If the vertically movable foot exerts excessive pressure on the measuring part, the nonwoven can be compressed, so that the wrong small thickness can also be read.

To avoid this unexpected risk, thickness measurements should be performed using a thickness meter with a vertically movable foot that applies a force of up to 95 g in total, with a flat specimen contact surface having a circular cross section of 0.5 cm or more in diameter. Measurement accuracy shall be at least ± 0.0005 cm. Although any device that meets these limitations is suitable for determining the thickness of a sample according to the present invention, several commercially available devices are also available. One such device found to be suitable for determining thickness in accordance with the present invention is a model PT223 Federal (Providence, equipped with a model PT223 contact foot loaded on a model 35B-8-R-1 stand). RI) C2l comparator. The thickness measurement should be the average of three or more readings taken at different points on the specimen.

The weight is determined using a laboratory balance with an accuracy of at least 0.0001 g.

Bicomponent fibers suitable for use in the nonwovens of the present invention are preferably bicomponent fibers in a side-by-side arrangement selected from the group consisting of PET / PPT, PET / PBT and PPT / PBT fibers. In the aforementioned group, the first crystallizable polyester component is listed first and the second crystallizable component is listed second. In other words, polymers that crystallize more slowly are listed first. Most preferably, the bicomponent fibers are bicomponent fibers in a side by side arrangement of PET / PPT.

A melt stream of PET having an intrinsic viscosity (IV) of 0.5 to 1.2 dl / g, preferably 0.7 to 0.9 dl / g, and an IV of 0.8 to 1.5 dl / g, preferably 0.9 to 1 dl / g Combining a melt stream of PPT and feeding the combined stream to the porous spinneret, wherein the single bicomponent strand is extruded at a temperature of 265 to 285 ° C., preferably 265 to 270 ° C., for use in the nonwoven fabric of the present invention. PET / PPT fibers can be prepared. The extrudate is recovered and quenched and then wound up without going through the stretching step. The winding speed, which is synonymous with the spinning speed in this case, is 2000 to 3500 m / min, preferably 2500 to 3000 m / min. After spinning, the yarns are cut into lengths of 3 to 25 mm, preferably 25 mm. I.V. was determined in p-chlorophenol at 25 ° C.

The preferred fibers thus prepared are then treated according to the process of the invention already described to produce the nonwoven fabric of the invention.

The nonwoven fabric of the present invention is particularly useful in fields such as particulate filtration and protective applications because of its high density and high resilience. Nonwoven fabrics are an ideal candidate for industrial dust removal applications because the random fiber arrangement of nonwovens allows for rapid distribution of the carrier phase into individual flows. The majority of nonwovens are needle punched and are commonly known as "needle felts" having a density of about 0.2 g / cm 3. At the same density, the nonwovens of the present invention are expected to have excellent filtration efficiency because they readily allow three-dimensional random arrangement of fibers. The latter greatly promotes the formation of important "dust bridges" in order to quickly reduce the penetration of dust to extremely low levels.

In another embodiment, during the integration of the fibrous mat precursor, bicomponent fibers suitable for use in the present invention may be prepared from DuPont Company's Nomex® or Kevlar® fibers. By combining with the same polyaramid fibers, the strength, heat resistance and puncture resistance of the nonwoven fabric can be improved. In this embodiment, polyaramid staple fibers, which generally do not exhibit heat shrink, are mixed with bicomponent fibers suitable for the practice of the present invention to form fibrous mat precursors. During the expression of crimps according to the process of the present invention, the polyaramid fibers are combusted and entangled with the crimped bicomponent fibers, thereby forming a highly reinforced network of tangled fibers, which allows the polyaramid fibers and the nonwovens to bind strongly. Such tight bonding can be achieved without the use of binders conventionally used to make blends comprising polyaramid.

For example, surface modifiers and additives can be readily incorporated into the nonwovens of the present invention to provide antimicrobial and flame retardant properties. Other polymer fibers with or without potential crimps can be easily incorporated by blending with the bicomponent fibers of the practice of the present invention, in particular by combining the fibers in the water-slurry step of a preferred embodiment of the present invention. The addition of short polyaramid fibers is thought to improve, for example, flame retardancy and wear resistance.

Although the present invention will be described further, the present invention is not limited only to the following specific embodiments.

The fibers used in the examples below were bicomponent yarns in a side-by-side arrangement made of 50/50 ratio PET (Crystar 4415, IV = 0.54 ± 0.02) and PPT (CIDU, IV = 1.04 ± 0.03). As described in US Pat. No. 3,671,379 to Evans et al., Polymers can be prepared using standard extrusion blocks and spinneret packs well known in the art for the production of bicomponent fibers in a side-by-side arrangement. Melt spinning through a spinneret with 34 holes at 265-270 ° C. according to standard procedures.

The extrudate was cooled by passing the extrudate through a crossflow quench zone, 182.9 cm (72 inches) in length, with a room temperature quench air running at about 10 m / min perpendicular to the yarn path. This was then wound up at the speeds indicated in the specific examples without going through any separate stretching step. The thus gained straight without having a noticeable crimp.

After spinning, the yarns were rewound to a length of 90 m each on a small motor-driven skater 11 cm in diameter. Each thread was then cut with scissors to a short fiber floc with the length indicated in the particular example. A solution of 5 g of F-98 Prill, commercially available surfactant from BASF Corp., Mountain Olive, NJ, dissolved in 2 liters of water was used for a Williams standard pulp tester measuring 28 cm x 28 cm x 28 cm. Poured into the receptor. Additional cold water was added to the vessel and filled. 6 g of floc were then carefully added to the pulp apparatus with a spatula and the aqueous slurry was stirred for about 30 seconds with a portable stirrer consisting of a wide steel plate with holes. Much care has been taken to avoid disturbances that inevitably result in flocculation. The water mat was then deposited to deposit a fiber mat on the porous cloth at the bottom of the receiver.

The fabric and fiber mat were then transferred onto a sheet dryer made by Williams Apparatus, Watertown, NY. The sheet dryer shown in FIG. 1 consists of a porous metal drum 1, on which up to half or less of the circumference of the porous metal drum is placed a cloth and a fiber mat 2. In order to fix the mat in place, the canvas sheet 3 fixed to one end 4 on the drum surface is covered on the fabric and fiber mat 2 and the handle 5 to which the other end of the canvas sheet is attached is attached. Tighten by rotating. By rotating the handle by hand to the desired degree of tightening, the pressure exerted on the fabric and the fiber mat by the canvas sheet can be varied in a somewhat subjective but wide range.

The mat was dried at 35 to 40 ° C. Drying was performed by applying slight pressure by tightening the canvas sheet cover by turning the handle about 2 times. After drying for 1 hour, the mat was recovered and cut into square samples of 3 " x3 " (7.62 cm x 7.62 cm). Each sample was then individually inserted between two 16 cm by 21 cm by 0.7 cm Teflon-coated aluminum plates, each weighing 554 g. The spacing between the plates was adjusted by inserting wedges having a thickness of 0.25-4 mm. The composite (2 plates + sample + wedge) was then heated for about 30 minutes with hot air at 120 ° C.

All mechanical tests were performed using a tabletop Instron Tensile Tester Model 1123. The device has been upgraded as an MTS Renew Package with MTS Testworks software version 4.0.

The crimp shrinkage (CC) of the yarns used in the process of the present invention was evaluated as follows: A 40.2 cm yarn piece was heated in 120 ° C. hot air for 30 minutes. The lengths of the yarns under 1.5 mg / d load L _1.5 and the lengths of yarns under 100 mg / d load L ₁₀₀ are indicated, and CC (%) = [ The crimp shrinkage was calculated by the formula (L ₁₀₀ -L _1.5 ) / L ₁₀₀ ] x 100. Three specimens were averaged to obtain a result.

To determine the number of crimps per centimeter (number of crimps per 0.39 inch), a separate yarn specimen was heated as in the crimp shrinkage test. This was then sandwiched between two glass plates and inspected at a magnification of about 16 × using a stereoscope with top illumination. The number of crimps per centimeter was determined by calculating the number of peaks on one fiber axis for the portion between the ends of 1 cm (0.39 inch).

Density was determined by measuring the thickness of a 3 "by 3" (7.62 cm by 7.62 cm) square swatch using a Fed C2l comparator loaded on a stand (Model 35B-8-R-1). The comparator had a flat contact point model PT223 applying a foot diameter of 0.18 "(0.46 cm) and a total force of 93 ± 2 g. The thickness was the average of five values taken at different points on the specimen.

The weight of the nonwoven specimen was determined using a Mettler 8200 balance with an accuracy of 0.0001 g.

Prior to the heat treatment, a typical wet-integrated sheet made of 0.64 cm (1/4 ") flocs had a thickness of 0.28 ± 0.02 mm.

The area shrinkage was measured for the entire sample using 100 * ( _before A- _after A) / ( _before A) ( _before A and _after A represent the area of the square sample _before and _after shrinkage).

Example 1

According to the process described above, 34 filament 50/50 PET / PPT bicomponent yarns with 5.9 denier / filament were spun at a rate of 3030 m / min. This bundle showed a tensile strength of 1.6 g / denier. The yarn thus prepared was cut to 1 inch (2.54 cm) floes with scissors and treated with hot air as a heating agent in a Williams standard pulp test apparatus using the method described above. Crimp shrinkage (CC), number of crimps per cm (number of crimps per 58 inches), and an average radius of curvature of 0.13 mm.The properties of the nonwovens for different wedge thicknesses are specified in Table I. Each value is two The average value for the sample The product of elastic modulus and elongation (called toughness) had a constant value of about 2.

wedge
(Mm) Area shrinkage (%) Surface density
(g / ㎡) Modulus
(g / d) % Elongation at full load Modulus of elasticity X elongation
(g / d ×%) density
(g / cm3) 0.25 44 226 0.055 35 1.9 0.28 0.50 58 179 0.045 50 2.2 0.24 One 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

Using the materials and processes of Example 1, except that the 2.54 cm (1 ") flocs were completely immersed in a 1% w / w aqueous solution of polyethylene oxide (Mw = 900,000) prior to dispersion in a Williams standard pulp test apparatus. The results are shown in Table II.

wedge
(Mm) Area shrinkage (%) Surface density
(g / ㎡) Modulus
(g / d) % Elongation at full load Modulus of elasticity X elongation
(g / d ×%) density
(g / cm3) 0.25 48 163 0.053 34 1.8 0.26 0.50 47 180 0.046 44 2.0 0.24 One 72 270 0.029 58 1.7 0.24 2 79 422 0.017 93 1.6 0.22 4 86 552 0.012 120 1.5 0.22

Example 3

The materials and processes of Example 1 were used except that the fibers were cut to 0.64 cm (1/4 ") flocs. The results are shown in Table III.

wedge
(Mm) Area shrinkage (%) Surface density
(g / ㎡) Modulus
(g / d) % Elongation at full load Modulus of elasticity X elongation
(g / d ×%) density
(C2l measuring instrument)
(g / cm3) 0.25 49 144 0.038 28 1.1 0.24 0.50 67 204 0.024 48 1.2 0.24 One 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 materials and processes of Example 3 were used except that yarns were spun at a speed of 1850 m / min to obtain 4.7 denier / filament yarns with a tensile strength of about 1.17 g / d. Expressing potential crimps according to the method described above, the yarn had a crimp shrinkage (CC) of 0.42, a crimp number per centimeter (number of crimps per 17 inches) of 6.7, and an average radius of curvature of about 1.1 mm. The results are shown in Table IV. The flocs in this example were 0.64 cm in length.

wedge
(Mm) Area shrinkage (%) Surface density
(g / ㎡) Modulus
(g / d) % Elongation at full load Modulus of elasticity X elongation
(g / d ×%) density
(g / cm3) 0.25 0 68 0.10 3 0.3 0.18 0.50 0 70 0.09 4 0.4 0.19 One 8 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 processes of Example 1 were used except that the floc length was 51 mm. The results are shown in Table V.

wedge
(Mm) Area shrinkage (%) Surface density
(g / ㎡) Modulus
(g / d) % Elongation at full load Modulus of elasticity X elongation
(g / d ×%) 0.50 59 171 0.045 55 2.5 One 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 shows an example where potential crimps were removed by thermosetting the fibers with shrinkage suppressed at drying temperatures higher than 60 ° C.

Drying was performed at the various temperatures specified in Table VI, using the materials and processes of Example 3. However, unlike Example 3, in order to apply pressure to the fibrous mat and to inhibit the mobility of the fibers to prevent shrinkage, the canvas sheet covering the fibrous mat was very much tightened during drying. The yarns were spun at a rate of 3030 m / min, cut to 0.64 cm (1/4 ") flocs and heat treated in hot air using a 2 mm wedge.

Drying temperature (℃) Area shrinkage (%) Surface density
(g / ㎡) Modulus
(g / d) % Elongation at full load Modulus of elasticity X 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 processes of Example 3 were used except that the crimp expression step was performed in 95 ° C. water. The results are shown in Table VII. At large wedge thicknesses in excess of 1 mm, the sample broke in water.

wedge
(Mm) Area shrinkage (%) Surface density
(g / ㎡) Modulus
(g / d) % Elongation at full load Modulus of elasticity X elongation
(g / d ×%) density
(g / cm3) 0.25 28 94 0.027 24 0.6 0.27 0.50 40 125 0.056 22 1.2 0.28 One 75 302 0.024 31 0.7 0.33 2 - - - - - - 4 - - - - - -

Comparative Example 5

Same as Comparative Example 4, except that yarns were spun at a speed of 1850 m / min. The results are shown in Table VIII.

wedge
(Mm) Area shrinkage (%) Surface density
(g / ㎡) Modulus
(g / d) % Elongation at full load Modulus of elasticity X elongation
(g / d ×%) density
(g / cm3) 0.25 0 64 0.23 3 0.7 0.20 0.50 0 73 0.038 5 0.2 0.23 One 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 fabric comprising a plurality of entangled spiral crimped asymmetric bicomponent fibers comprising a first crystallizable polyester component and a second crystallizable polyester component, wherein the first crystallizable polyester component comprises the second crystallizable poly component. Exhibit a lower crystallization rate than the ester component, the fibers having a denier range of 0.5 to 6 denier, wherein the fibers have a crimp number per 1 centimeter or greater (number of crimps per inch or greater) and crimp less than or equal to 0.2 mm Exhibit a radius of curvature, the fibers are entangled with each other, further the fibers are oriented in a plane, and the nonwoven fabric has a bulk density of 0.2 to 0.4 g / cm 3. 2. The nonwoven fabric of claim 1, wherein said bicomponent fibers are bicomponent fibers in a side-by-side arrangement. 2. The nonwoven fabric of claim 1, wherein said first crystallizable polyester component is poly (ethylene terephthalate) and said second crystallizable polyester component is poly (propylene terephthalate). 2. The nonwoven fabric of claim 1, wherein said first crystallizable polyester component is poly (propylene terephthalate) and said second crystallizable polyester component is poly (butylene terephthalate). 2. The nonwoven fabric of claim 1, wherein said first crystallizable polyester component is poly (ethylene terephthalate) and said second crystallizable polyester component is poly (butylene terephthalate). The nonwoven fabric of claim 1, wherein the bicomponent fibers are staple fibers. 7. The nonwoven fabric of claim 6 wherein the first crystallizable polyester is poly (ethylene terephthalate) and the second crystallizable polyester is poly (propylene terephthalate), each ratio being from 70:30 to 30:70. . The nonwoven fabric of claim 7 wherein each ratio is from 60:40 to 40:60. The nonwoven fabric of claim 1 wherein the bicomponent fibers are continuous fibers. The nonwoven fabric of claim 1, further comprising an initial Young's modulus of 1.2 to 12 MPa and an ultimate elongation of 150% or less. Side-by-side with multiple tangled helical crimps comprising polyethylene terephthalate and polypropylene terephthalate in a ratio of 60:40 to 40:60 and having 0.5 to 6 denier and a non crimp length of 20 to 25 mm. A nonwoven fabric comprising staple bicomponent fibers in an array, the fibers exhibiting at least 19.7 crimps per centimeter (at least 50 crimps per inch) and a crimp radius of curvature of 0.2 mm or less, the fibers being entangled with each other, and further Wherein the fibers are oriented in a plane, the nonwoven fabric has a bulk density of 0.2 to 0.4 g / cm 3, an initial Young's modulus of 1.2 to 12 MPa and an ultimate elongation of 150% or less. A plurality of asymmetric bicomponent fibers comprising a first crystallizable polyester component and a second crystallizable polyester component and having potential crimps are disposed in a planar arrangement of the overlapping fibers, the asymmetric bicomponent fibers oriented in their plane A planar arrangement is disposed between the two constraint surfaces; Heating the planar arrangement such that at least a portion of the potential crimp is expressed, while forcing a nonwoven structure into contact with the restraining surface during at least a portion of the heating. 13. The method of claim 12, wherein the planar arrangement is in the form of a fibrous mat preform. 13. The method of claim 12, wherein said bicomponent fibers are bicomponent fibers in a side-by-side arrangement. 13. The method of claim 12, wherein said bicomponent fiber comprises a polyester. 13. The method of claim 12 wherein the first crystallizable polyester component is poly (ethylene terephthalate) and the second crystallizable polyester component is poly (propylene terephthalate). 13. The method of claim 12, wherein said first crystallizable polyester component is poly (propylene terephthalate) and said second crystallizable polyester component is poly (butylene terephthalate). 13. The method of claim 12 wherein the first crystallizable polyester component is poly (ethylene terephthalate) and the second crystallizable polyester component is poly (butylene terephthalate). 13. The method of claim 12, further comprising forming a fibrous mat prestructure from an aqueous slurry of flocs having an average length of 3 to 25 mm. Side-by-side, 20-25 mm in length, with a potential crimp shrinkage of 70-80%, comprising polyethylene terephthalate and polypropylene terephthalate at a ratio of 60: 40-40: 60, respectively. Forming a fibrous mat prestructure from an aqueous slurry of non-crimped staple bicomponent fibers in an array, and placing the fibrous mat prestructure between two restraining surfaces; Heating the fibrous mat prestructure such that at least a portion of the potential crimp is expressed, while forcibly contacting the fibrous mat prestructure with the restraining surface during at least a portion of the heating.

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