JP2006507417A - High stretch recovery nonwoven fabric and manufacturing method - Google Patents

Abstract

The present invention relates to a novel nonwoven fabric characterized by high elongation recovery and a method for producing said fabric by using latent crimpable fibers.

Description

  The present invention relates to a novel nonwoven fabric characterized by high elongation recovery and a method for producing said fabric by using latent crimpable fibers.

  Nonwoven fabrics made from thermoplastic synthetic fibers are well known in the art and are both available from DuPont Company, such as Tyvek (R) and Sontara (R). It is widely used for commercial purposes under various brand names.

  Bulky textile-like products with high stretch combined with high elongation recovery are awaited with nonwovens. Such fabrics are collectively known as “stretchable nonwoven fabrics”. Many approaches to the production of stretchable nonwovens have been taken.

  One approach to making stretchable nonwovens has been to use crimped staple fibers where the entanglement of crimped fibers provides the cohesive strength and recovery required by stretchable nonwovens. In some cases in the art, crimped fibers are formed into mats and interlaced through the use of air or water jets. In other cases in the art, a straight or substantially straight fiber with latent crimp is first formed into a mat, after which the latent crimp is realized by heating, thereby “entangled itself”. Create a structure. However, the stretch nonwovens of the art have poor toughness and density, defined as the product of tensile modulus and ultimate elongation, to be useful in many textile and industrial applications. It is the toughness of the fabric that determines its “stretchability,” the amount it can be stretched and its recovery force. The stretch nonwoven fabrics of the art are limited to low density or, in technical terms, very bulky fabrics with very low stretch.

Aranaga et al. (Patent Document 1) discloses a wet-lay method for forming a nonwoven fabric from a composite fiber of polyethylene terephthalate / polypropylene terephthalate having latent crimpability. The resulting nonwoven fabric is said to have a high percentage recovery. The wet-lay process involves hydroentangling the fibers to provide sufficient entanglement before developing crimps. The non-woven fabric produced thereby is characterized by a basis weight of 30 g / m ² with a 0.3 mm thick fabric. It has been recognized by Aronaga and elsewhere that high recovery crimped fibers have the potential to produce high value nonwovens. However, an obvious and perceived difficulty is that fibers with high shrinkage tend to crimp alone, reducing entanglement formation and increasing fabric bulk. It is also often associated with fabric breakage during shrinkage. The result is a high bulk fabric that is typically suitable for applications that are not subjected to loads, and the full potential of high recovery fibers is not realized.

Furukawa, U.S. Pat. No. 6,057,028 discloses a very bulky nonwoven having a bulk density of less than 0.020 g / cm < ³ > formed from crimped polyolefin composite staple fibers. Crimp frequencies greater than 12 crimps per inch are said to be detrimental to web formation because it makes the web density too high. Furukawa structures are said to be “melt bonded” by thermal bonding, and rather than fiber entanglement, said melt bonding is said to be the main mechanism holding the structure together. .

  Stokes, et al. (US Pat. No. 5,639,097) disclose a method for forming a bulky nonwoven fabric with high compression resistance from crimped composite polyolefin fibers followed by cross-linking to maintain elasticity.

Terakawa et al. (US Pat. No. 5,697,049), air-entangled as-spun yarn bundles with latent crimps, heats to a temperature at which crimps develop, and heats to a temperature that causes joining at the intersection. A method for producing a nonwoven fabric from continuous composite polyolefin fibers is disclosed. The nonwoven fabric by Terrakawa has a density below 0.030 g / cm ³ .

  Shawver et al., U.S. Pat. No. 5,677,086, discloses a stretchable nonwoven made from a spunbond material laminated to an elastomeric inner layer sheet.

  Pike et al., U.S. Pat. No. 6,037,049, describes a continuous multicomponent thermoplastic having latent crimpability and crimped to varying degrees in air prior to the formation of a thermally bonded nonwoven web. The formation of nonwoven webs from fibers, especially polyolefins, is disclosed.

JP-A-11-158733 US Pat. No. 4,469,540 International Publication No. 00/18995 Pamphlet European Patent No. 0 391 260 B1 US Pat. No. 5,540,976 US Pat. No. 5,418,045 US Pat. No. 3,338,992 U.S. Pat. No. 3,671,379

The present invention is a nonwoven fabric comprising a plurality of entangled helically crimped asymmetric composite fibers comprising a first crystalline polyester component and a second crystalline polyester component, wherein the first crystalline polyester component is the first crystalline polyester component. At least 50% per inch, exhibiting a slower crystallization rate than the bicrystalline polyester component, wherein the fiber is characterized by a denier range of 0.5-6 denier, and the fiber has a crimp radius of curvature of 0.2 mm or less. The fibers are mainly entangled with each other, and the fibers are mainly oriented in a well-defined plane, and the nonwoven fabric has a bulk of 0.2 to 0.4 g / cm ³ Provide a non-woven fabric characterized by density.

  The present invention further includes the step of disposing a plurality of asymmetric composite fibers having latent crimpability in a planar array of overlapping fibers, wherein the fibers are mainly oriented in the plane, and the planar array is divided into two Between the constraining surfaces and at least part of the heating, heating the planar array on the condition that the non-woven structure is in constraining contact with the constraining surfaces to provide at least the latent crimpability And a method of forming a nonwoven fabric.

In the art, a planar array of conjugate fibers with latent crimpability, typically a fiber mat, is manufactured and subsequently heated to develop crimps, thereby entangle the fibers and create a stable nonwoven structure It is known to produce non-woven fabrics. Throughout the crimping process, the fiber mat or other structure undergoes contraction in the plane with simultaneous expansion in a direction perpendicular to the plane. As a result, the nonwovens of the art are in a very low bulk density, generally well below 0.1 g / cm ³ . As a result, they have limited utility in many textile applications that require high toughness or high elongation recovery.

  The present invention is based on the discovery that entanglement between high crimp and high recovery fibers can be facilitated by careful control of fabric expansion perpendicular to the plane of the fabric during the crimp development process. In the state of the art, the occurrence of crimp usually leads to a large contraction in the plane with involuntary expansion in a direction perpendicular to the plane.

  In the method of the present invention, a plurality of asymmetric composite fibers having latent crimpability in the first step are arranged to form a planar array of the fibers, wherein the fibers are mainly oriented in the plane, where overwhelming A number of said fibers are in cross contact with at least one other said fiber. The planar array in a preferred embodiment is referred to herein as a “fiber mat preform” to indicate the nonwoven structure prior to undergoing the second step of the method of the present invention, the crimping step. The crimping step is performed by heating the planar array to develop crimps while the planar array is disposed between two constraining surfaces that are oriented at least approximately parallel to the plane of the planar array. The separation of the two constraining surfaces is adjusted so that during at least some part of the crimping process, the expansion of the planar array perpendicular to the plane is constrained by simultaneous contact with both constraining surfaces. This contact during the expansion process introduces a compressive force on the shrinking array. The resulting nonwovens exhibit higher density and stronger physical properties than nonwovens made from comparable starting materials and made without constraining expansion perpendicular to the plane.

  A composite fiber suitable for the method of the present invention is preferably present in two continuous phases in contact with each other, wherein the two phases exhibit a different contraction from the other, thereby allowing the development of a helical crimp upon contraction, preferably Are fibers containing two polymers of the same genus group. The phases may be arranged in a side-by-side or asymmetric sheath-core arrangement. Side by side is preferred. Suitable composite fibers include, but are not limited to, composite polyesters, composite polyamides, and composite polyolefins. Polyester is preferred. Included therein are copolymers of these broad classes of polymers. Among the polyesters, preferred types of composite fibers include polyethylene terephthalate (PET) / polypropylene terephthalate (PPT), PET / polybutylene terephthalate (PBT), and PPT / PBT, with PET / PPT being preferred.

  Also encompassed by the term “composite” are fibers sometimes referred to as bicomponents comprising polymers from different groups, such as polyamides and polyesters. However, bicomponent fibers are less preferred.

  For purposes of this invention, latently crimpable fibers typically heat at least one of the components above their glass transition temperature by taking advantage of the difference in shrinkage behavior of the two components. This is a fiber that has the inherent ability to develop additional crimps. Latent crimped fibers may exhibit some or no crimps. In the practice of the present invention, the latent crimpable fibers are preferably flat and free of crimps.

  The inventors of the present invention, for example, the expansion of the fabric in a direction perpendicular to the plane, such as by crimping with a fabric placed between two metal plates parallel to the plane of the fiber mat preform. It has been discovered that when crimp expression is performed under conditions where is constrained, the result is that the fabric is subjected to considerable densification, making the individual fibers more highly entangled. The result is a dense, tough fabric with improved stretch recovery over fabrics made by prior art methods starting from the same fiber mat preform.

  The degree of densification and characteristics that can be achieved are not only the starting bulk density of the planar array, the extent to which the fibers overlap each other, and the separation distance between the constrained surfaces, but also the specific type used in the present invention. It will depend on the crimp shrinkage of the fiber. If others are equal, higher crimp shrinkage, greater degree of inter-fiber overlap, higher starting bulk density, and narrower gaps between constraining surfaces (fibers can no longer slip, and crimping is All up to the point of significant hindrance) is related to higher density nonwoven products, higher toughness, and higher elongation recovery.

  The benefits of the method of the invention are quite general and apply to the production of nonwovens of essentially any composition, provided that composite fibers with latent crimp are used in the planar array of overlapping fibers. May be.

  The fibers used in the present invention may be in the form of continuous or long fibers, or they may be staple fibers. Continuous fibers may be spun in the form of multifilament yarns, but are preferably deposited as individual fibers to form a fiber mat precursor. Staple fibers are preferred, fibers of fiber denier in the 3-25 mm length range and in the range of 0.5-6 denier per filament (dpf). In a preferred embodiment, the fibers are PET and PPT composite staple fibers in a concentration ratio of 70:30 to 30:70, respectively, preferably 60:40 to 40:60, respectively.

  In a more preferred embodiment, the fibers used in the present invention are uncrimped staple PET / PPT bicomponent fibers having a latent crimp shrinkage of at least 40%, preferably 70-80%. Both PET and PPT are crystalline polymers. However, PPT shows a higher crystallization rate than PET.

  Preferred PET / PPT fibers for use in the present invention have a melt flow of PET having an intrinsic viscosity (IV) of 0.4 to 0.8, preferably 0.5 to 0.6, 0.8 Of 1.5 to 1.5, preferably 0.9 to 1.0. V. In combination with a melt flow of PPT having the following: feed the combined stream to a porous spinneret and extrude it from 260 ° C. to 285 ° C., preferably 265 ° C. to 270 ° C. The extrudate is collected, quenched, and then wound without a stretching step. The spinning speed is in the range of 1900-3500 m / min, preferably 2000-3000 m / min. After spinning, the yarn undergoes cutting to a length of 3-25 mm, preferably a length of 20-25 mm. I. V. Is measured at 25 ° C. in p-chlorophenol.

  The practitioner will understand that the specific value of spinning speed that gives the desired fiber properties depends on the specific choice of polymer used, spinning temperature specifications, fiber diameter, and type of quenching. The practitioner will further appreciate that the spinning speed range suitable for PET / PPT fibers is different from the spinning speed range suitable for other compositions. For example, for PET / PBT fibers, the operating range is about 1700-3200 m / min, preferably 1800-3000 m / min, and for PPT / PBT fibers the operating range is 600-2000 m / min, preferably 800-1600 m / min. I understood that.

  The staple fiber yarn so produced is then water with a solids content in the range of 0.05 g / l to 1 g / l, preferably 0.25 g / l to 0.75 g / l with the aid of a surfactant. To be distributed. The dispersion is agitated without causing turbulence to obtain a homogeneous, well-separated mixture of fibers. The fiber dispersion is then deposited on a 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 accomplished while wiping the surface.

Other means and media for dispersing the fibers may be used. The fibers may be dispersed using a liquid other than water as long as the liquid is essentially inert. Or fibers can be dispersed in a gaseous medium such as air, or supercritical CO _2. However, an aqueous dispersion method using techniques similar to those of known papermaking methods is most convenient and is therefore preferred.

  In an alternative embodiment of the present invention, the fiber is in the form of a continuous multifilament yarn with latent crimpability. When such continuous filaments are used, a high degree of filament separation must occur in order to form a planar array or fiber mat precursor suitable for the method of the present invention. One way to achieve such filament separation is to charge the yarn bundle with static electricity. The moving multifilament yarn bundle is electrostatically charged to a potential sufficient to separate each filament from adjacent filaments, and then during such separation, the filaments are collected as a random nonwoven web. Preferred yarns have zero twist or crimp to achieve maximum filament separation. The minimum level of charge is 30,000 electrostatic units (esu). Until such tension is removed, i.e. under sufficient tension such that they do not separate until after they have been pushed towards the receiving surface on which the planar array is to be formed. Charging is accomplished, so that the filaments are separated immediately. The filament may be charged by corona discharge, by triboelectric contact, by electric field charging, or by other suitable methods. In one embodiment, newly formed synthetic organic filaments formed according to the method of the present invention are charged by passing a high intensity electric field while still above their solidification temperature. A suitable apparatus and detailed procedure for charging a yarn bundle suitable for the practice of the present invention is described in US Pat. The filaments that make up such treated yarns are laid down to form an overlapping pattern, producing a planar array or fiber mat precursor in which the filaments are primarily oriented in that plane.

  The planar array of continuous fibers so produced is then conveyed to the heating zone in a continuous or batch continuous process where latent crimps are developed and the nonwoven fabric of the present invention is produced. Although many methods for providing heating are known in the art, any method suitable for the practice of the present invention will necessarily involve a constrained expansion perpendicular to the plane of the precursor fabric. Such methods would include batch type methods such as a fixed heating zone between two plates, or continuous process methods such as calendering or heated conveyors. The method of achieving the desired crimp is not critical as long as it satisfies the condition that the nonwoven structure is in constraining contact with the constraining surface during at least a portion of the heating.

  Heating to develop the potential crimpability of the fibers in the nonwoven structure so produced may be accomplished using a variety of methods that are well within the purview of those skilled in the art. . Satisfactory results are achieved by (i) heating at a temperature above 80 ° C. in hot air, such as in a forced convection hot air oven, preferably at about 120 ° C., or (ii) at a temperature of about 95 ° C. in water. It has been found in the practice of the present invention. In a typical implementation of the method of the invention, crimp development occurs within seconds after the indicated heat exposure. Hot air is a preferred heating medium when the distance between the constraining surfaces exceeds about 2 mm. It can be seen in the practice of the invention that hot water heating of samples thicker than about 2 mm often results in sample crushing.

  In a further embodiment, it is an object of the present invention to provide entangled nonwovens with high toughness and controlled properties ranging from high stretch / low stiffness to high stiffness / low stretch. This is obtained by (i) using highly latent crimpable fibers and (ii) suppressing fabric thickness expansion during thermally induced area shrinkage according to the method of the present invention as described herein. It is done. Area shrinkage during crimp development is an indicator of the degree of crimp development.

The nonwoven fabric of the present invention has a particularly desirable property of toughness, defined as the product of the Young's modulus and its ultimate elongation. When a nonwoven is produced according to a preferred embodiment of the method of the present invention, a fabric is produced that exhibits an initial Young's modulus value in the range of 1.2-12 MPa and an ultimate elongation of up to 150%. A preferred embodiment of the nonwoven fabric of the present invention is a fabric having a bulk density of 0.20 to 0.28 g / cm ³ , with ultimate elongation and tension ranging from about 30% and 6 MPa to 100% and 1.8 MPa, respectively. Provides a combination of elastic moduli.

The nonwoven fabric of the present invention is a side-by-side type composite fiber crimped into a plurality of entangled spirals containing a first crystalline polyester component and a second crystalline polyester component, wherein the first crystalline polyester component is the first crystalline polyester component. Exhibit at least 50 crimps per inch with a crimp radius of curvature of 0.2 mm or less, characterized by a denier range of 0.5 to 6 dpf, exhibiting a slower crystallization rate than a bicrystalline polyester component And are further characterized by a bulk density of 0.2-0.4 g / cm ³ , which further includes fibers that are entangled with each other and that are primarily oriented in a well-defined plane.

The density of the nonwoven fabric of the present invention is determined by cutting a specimen having a known area, measuring its thickness and its weight, and formula δ (density) = weight (g) / (area (cm ² ) × thickness (cm) )
The density is calculated by computer calculation.

  The nonwoven fabric of the present invention is easily compressed and provides many gaps between the fibers. Therefore, obtaining an accurate measurement of thickness to make an accurate measurement of density is problematic. Normally, the thickness of objects such as film and cloth is measured in the art by the use of a contact thickness meter, where the specimen to be measured displays a fixed anvil and thickness. Placed between a vertically movable foot attached to a means for. If the vertically movable foot has a too narrow cross section, it may slip between adjacent fibers, thereby incorrectly giving a low thickness reading. If the vertically movable foot places excessive pressure on the area being measured, it may result in fabric compression and again, erroneously resulting in a low thickness reading.

  In order to avoid these pitfalls, the thickness measurement has a vertically movable foot with a flat specimen contact surface with a circular cross section of at least 0.5 cm diameter and a thickness applying a total force of 95 g or less. Should be done using a meter. Thickness accuracy should be at least ± 0.0005 cm. Although any instrument that meets these limitations is suitable for measuring the thickness of a sample according to the present invention, several satisfactory commercially available instruments are available. One such instrument that has been found suitable for thickness measurement according to the present invention is model PT223 Federal (Rhode Island) with a model PT223 contact foot attached to a model 35B-8-R-1 stand. Providence (RI) C2I comparative length meter (Comparator) meter. The thickness measurement should represent the average of at least three readings taken at different points on the specimen.

  The weight is measured with a laboratory balance having an accuracy of at least 0.0001 g.

  The conjugate fiber suitable for use in the nonwoven fabric of the present invention is preferably a side-by-side conjugate fiber selected from the group consisting of PET / PPT, PET / PBT, and PPT / PBT fibers. Within the preceding group, the first crystalline polyester component is listed first and the second crystalline component is listed second. In other words, polymers that are slower to crystallize are listed first and polymers are listed. Most preferably, the conjugate fiber is a PET / PPT side-by-side conjugate fiber.

  Preferred PET / PPT fibers for use in the nonwoven fabric of the present invention have a melt flow of PET having an intrinsic viscosity (IV) of 0.5 to 1.2, preferably 0.7 to 0.9, 0 .8 dl / g to 1.5 dl / g, preferably 0.9 to 1. V. In combination with a melt flow of PPT having a single composite at a temperature of 265 ° C. to 285 ° C., preferably 265 ° C. to 270 ° C. from the spinneret. Strands are extruded from their respective holes. The extrudate is collected, quenched, and then wound without a stretching step. In this case, the winding speed, which is synonymous with the spinning speed, is in the range of 2000-3500 m / min, preferably 2500-3000 m / min. After spinning, the yarn undergoes a cut to a length of 3 to 25 mm, preferably a length of 25 mm. I. V. Is measured at 25 ° C. in p-chlorophenol.

  The preferred fibers so produced are then processed according to the method already described, resulting in the nonwoven fabric of the present invention.

The unusually high density and high resiliency of the nonwoven fabrics of the present invention makes them useful in areas such as fine grain filtration and protective applications. Nonwoven fabrics are ideal candidates for industrial dust removal applications because their random arrangement of fibers allows for rapid distribution of the carrier phase into individual streams. The majority of nonwovens are needle punched and are commonly known as “needle felts” with a density of about 0.2 g / cm ³ . At the same density, the fabric of the present invention is expected to have excellent filtration efficiency as it easily provides a three-dimensional random arrangement of fibers. The latter greatly facilitates “dust bridge” build-up, which is very important for rapidly reducing dust penetration to very low levels.

  In another embodiment, a bicomponent fiber suitable for use in the present invention is obtained from DuPont Company, preferably during fiber mat precursor laydown, to increase the strength, heat resistance and penetration resistance of the resulting fabric. It may be combined with polyaramid fibers such as possible Nomex® or Kevlar® fibers. In this embodiment, polyaramid staple fibers that generally do not exhibit thermal shrinkage are blended with bicomponent fibers suitable for the practice of the present invention to form a fiber mat precursor. During crimp development according to the method of the present invention, the polyaramid fibers are entangled with twisted and crimped composite fibers to form a highly reinforced network of entangled fibers, and the polyaramid fibers are firmly attached to the nonwoven fabric. Combine. This tight coupling can be achieved without the use of binders as commonly used in the manufacture of blends containing polyaramid.

  For example, surface modifiers and additives can be easily incorporated into the nonwoven fabrics of the present invention to provide antibacterial and flame retardant properties. Other polymer fibers that show or do not show latent crimp are also easily incorporated by blending with composite fibers in the practice of the invention, particularly by combining the fibers in the water slurry stage of the preferred embodiment of the invention. Can do. The addition of short polyaramid fibers may be considered to improve, for example, flame retardancy and abrasion resistance.

  The invention will be further described in the following specific embodiments, but is not limited thereto.

  The fibers used in the following examples are 50/50 ratio PET (Crystar 4415, IV = 0.54 ± 0.02) and PPT (CIDU), IV = 1.04 ± 0.03. ) Composite side-by-side type yarn. Polymers are well known in the art for producing side-by-side composite fibers, according to standard procedures in the art and as described in Evans et al., US Pat. Melt spinning was performed with a 34-hole spinneret at 265-270 ° C. using an extrusion block and spinneret pack.

  The extrudate was cooled with a stream of room temperature quench air moving perpendicular to the yarn path at approximately 10 m / min by passing through a 72 inch long cross flow quench zone. It was then wound at the speed shown in the specific examples without any separate stretching step. The resulting yarn was straight, i.e. it did not show any visible crimp.

  After spinning, the yarn was rewound by a length of 90 m each on a small motor driven skein machine with a diameter of 11 cm. Each skein was then cut with scissors into short fiber flocs of the length shown in the specific examples. A solution of 5 grams of F-98 Prill (surfactant available from BASF Corp., Mt. Olive, NJ) in 2 liters of water, dimensions 28 cm × 28 cm × Pour into the reservoir of a Williams Standard Pulp Testing Apparatus having a 28 cm length. Additional cold water was added to fill the reservoir. 6 g of floc was then gently dispersed in the pulp apparatus using a spatula and the aqueous slurry was agitated for about 30 seconds using a portable agitator consisting of a wide steel plate with holes in it. High care must be taken to avoid turbulence that inevitably leads to agglomeration. The water was then drained, thereby depositing the fiber mat on the porous cloth at the bottom of the reservoir.

  The cloth and fiber mat were then transferred onto a sheet dryer also manufactured by Williams Apparatus, Watertown, NY. The sheet dryer shown in FIG. 1 is composed of a porous metal drum 1, and a cloth and a fiber mat 2 are arranged over half of the circumference of the drum. In order to fix the mat in place, the canvas sheet 3 fixed at one end 4 on the surface of the drum is placed on one side of the cloth and the fiber mat 2, and the knob 5 to which the other end of the canvas sheet is attached is turned. Tighten with. By manually turning the knob to the desired degree of tightening, the pressure applied to the cloth and fiber mat by the canvas sheet may vary over a wide range, albeit somewhat subjective.

  The mat was dried at 35 ° C to 40 ° C. Drying took place under the slight pressure obtained by tightening the canvas covering the sheet by approximately two turns of the knob. After 1 hour of drying time, the mat was removed and cut into square 3 inch x 3 inch samples. Each sample was then individually inserted between two 16 cm × 21 cm × 0.7 cm Teflon-coated aluminum plates, each weighing 554 g. The distance between the plates was controlled by inserting shims with thicknesses varying from 0.25 to 4 mm. Next, the composite (2 plates + sample + shim) was heated with hot air at 120 ° C. for about 30 minutes.

  All mechanical tests were performed using a table top Instron tensile tester, model 1123 (Instron Tensile Tester, Model 1123). The machine was upgraded with an MTS update package (Renew Package) that included MTS Works software version 4.0.

The crimp shrinkage (CC) of the yarn to be used in the method of the present invention was evaluated as follows. A 4-inch piece of yarn was heated in hot air at 120 ° C. for 30 minutes. Next, the piece was hung from the hook at its midpoint, thereby forming a loop, and the two ends were bonded together with tape. When the length of the thread under 1.5 mg / d load attached to the end bonded with the tape is indicated by L _{1.5 and} that under 100 mg / d load is indicated by L ₁₀₀ , the crimp contraction is CC (% ) = [(L ₁₀₀ −L _1.5 ) / L ₁₀₀ ] × 100. Results were obtained by averaging three test pieces.

  To measure the number of crimps per inch (CPI), separate specimens of the yarn were heated as in the crimp shrinkage test. Next, it was sandwiched between two glass plates and inspected using a stereoscope with peak light at a magnification of about 16 times. The CPI number was obtained by calculating the number of peaks on one side of the fiber axis over a section with end distance equal to 1 inch.

  Density measured 3 inch x 3 inch (7.62 cm x 7.62 cm) square specimen thickness using a federal C2I comparative length measuring instrument attached to a stand (model 35B-8-R-1) Sought by. The comparative length gauge has a flat contact point model PT223 that applies a total force of 93 ± 2 g and a foot diameter of 0.18 inches (0.46 cm). The thickness was the average of five measurements at different locations on the specimen.

  The weight of the fabric specimen was measured using a Mettler 8200 scale with an accuracy of 0.0001 g.

  Prior to heat treatment, a typical wet laid sheet made of ¼ inch floc has a thickness of 0.28 ± 0.02 mm.

The area shrinkage was measured for the entire sample using the relationship 100 × ( _before A− _after A) / ( _before A) (where, _before A and _after A represents the area of the square sample _before and _after shrinkage).

Example 1
A 34 filament 50/50 PET / PPT composite yarn having 5.9 denier per filament was spun at a speed of 3030 m / min according to the method described hereinabove. The yarn bundle exhibited a tensile strength of 1.6 grams / denier. The yarn so produced was cut into 1 inch flocs with scissors and processed on a Williams standard pulp tester using the method described hereinabove, using hot air as the heating agent. The resulting crimped yarn had the following characteristics: Crimp shrinkage CC = 74%, average radius of curvature of 0.13 mm, number of crimps per inch CPI = 58. The properties of the fabric are shown in Table I for different shim thicknesses. Each value was an average over two samples. The product of elastic modulus and elongation (referred to as toughness) had a constant value of about 2.

(Example 2)
Example 1 except that 1 inch floc was thoroughly moistened in a 1% w / w solution of polyethylene oxide in water (Mw = 900,000) prior to dispersion in the Williams standard pulp test equipment. The materials and procedures were repeated. The results are shown in Table II.

(Example 3)
The material and procedure of Example 1 was repeated except that the fiber was cut to 1/4 inch floc. The results are shown in Table III.

(Comparative Example 1)
The method and materials of Example 3 were repeated except that the yarn was spun at 1850 m / min resulting in 4.7 denier per filament yarn with a tensile strength of about 1.17 g / d. When developing its potential crimpability according to the method outlined herein above, the yarn has the following properties: crimp shrinkage CC = 0.42, number of crimps per inch with an average radius of curvature of 1.1 mm. CPI = 17. The results are shown in Table IV. The floc in this comparative example was 0.64 cm long.

(Comparative Example 2)
The material and method of Example 1 were repeated except that the floc length was 51 mm. The results are shown in Table V.

(Comparative Example 3)
This comparative example illustrates that at drying temperatures higher than 60 ° C., shrinkage constrained fibers undergo heat setting, thereby eliminating latent crimpability.

  The material and procedure of Example 3 was repeated with drying at various temperatures as shown in Table VI. However, unlike Example 3, pressure was applied to the fiber mat to restrain the fiber mobility and thereby tightly tighten the canvas sheet covering the fiber mat during drying to prevent shrinkage. The results are for yarns spun at 3030 m / min, cut to 1/4 inch floc and then heat treated in hot air using a 2 mm shim.

(Comparative Example 4)
The material and procedure of Example 3 was repeated except that the crimping stage was performed in 95 ° C. water. The results are shown in Table VII. The sample broke in water with a large shim thickness> 1 mm.

(Comparative Example 5)
Same as Comparative Example 4, but the yarn was spun at 1850 m / min. The results are shown in Table VIII.

8 depicts the placement of the wet fiber mat precursor and cross support on the drying drum of the Williams Pulp Test Equipment.

Claims (20)

A non-woven fabric comprising a plurality of entangled helically crimped asymmetric composite fibers comprising a first crystalline polyester component and a second crystalline polyester component, wherein the first crystalline polyester component is the second crystalline polyester Exhibit at least 50 crimps per inch, exhibiting a slower crystallization rate than the component, wherein the fibers are characterized by a denier range of 0.5-6 denier, and the fibers have a crimp radius of curvature of 0.2 mm or less; The fibers are mainly entangled with each other, and the fibers are mainly oriented in a well-defined plane, and the nonwoven fabric is characterized by a bulk density of 0.2-0.4 g / cm ³ A non-woven fabric characterized in that   The nonwoven fabric according to claim 1, wherein the conjugate fiber is a side-by-side conjugate fiber.   The nonwoven fabric according to claim 1, wherein the first crystalline polyester component is poly (ethylene terephthalate) and the second crystalline polyester component is poly (propylene terephthalate).   The nonwoven fabric according to claim 1, wherein the first crystalline polyester component is poly (propylene terephthalate) and the second crystalline polyester component is poly (butylene terephthalate).   The nonwoven fabric according to claim 1, wherein the first crystalline polyester component is poly (ethylene terephthalate) and the second crystalline polyester component is poly (butylene terephthalate).   The nonwoven fabric according to claim 1, wherein the conjugate fiber is mainly staple fiber.   The first crystalline polyester is poly (ethylene terephthalate) and the second crystalline polyester is poly (propylene terephthalate) at a concentration ratio in the range of 70:30 to 30:70, respectively. The nonwoven fabric according to claim 6.   The nonwoven fabric according to claim 7, wherein the concentration ratio is in the range of 60:40 to 40:60, respectively.   The nonwoven fabric according to claim 1, wherein the composite fiber is continuous.   The nonwoven fabric of claim 1 further characterized by an initial Young's modulus of 1.2-12 MPa and an ultimate elongation of up to 150%. In a plurality of interlaced spirals of polyethylene terephthalate and polypropylene terephthalate in a concentration ratio in the range of 60:40 to 40:60, with an uncrimp length in the range of 0.5-6 denier and in the range of 20-25 millimeters A non-woven fabric comprising crimped side-by-side composite staple fibers, wherein the fibers have a crimp radius of curvature of 0.2 mm or less, exhibit at least 50 crimps per inch, and the fibers are primarily entangled with each other; In addition, the fibers are primarily oriented in a well-defined plane, with a bulk density of 0.2-0.4 g / cm ³ , an initial Young's modulus of 1.2-12 MPa, and an extreme up to 150% Nonwoven fabric characterized by elongation.   Arranging a plurality of asymmetric composite fibers having latent crimpability in a planar array of overlapping fibers, wherein the fibers are primarily oriented in that plane and the planar array is disposed between two constraining surfaces And at least a part of heating, the planar array is heated under the condition that the nonwoven structure is in constraining contact with the constraining surface to develop at least a part of the latent crimpability. A process for forming a nonwoven fabric comprising the steps of:   13. The method of claim 12, wherein the planar array is in the form of a fiber mat preform.   The method according to claim 12, wherein the composite fiber is a side-by-side type composite fiber.   The method of claim 12, wherein the composite fiber consists essentially of polyester.   The method of claim 12, wherein the first crystalline polyester component is poly (ethylene terephthalate) and the second crystalline polyester component is poly (propylene terephthalate).   The method of claim 12, wherein the first crystalline polyester component is poly (propylene terephthalate) and the second crystalline polyester component is poly (butylene terephthalate).   The method of claim 12, wherein the first crystalline polyester component is poly (ethylene terephthalate) and the second crystalline polyester component is poly (butylene terephthalate).   The method of claim 12, further comprising forming a fiber mat preform from an aqueous slurry of floc having an average length of 3 to 25 millimeters. A fiber mat preform is formed from an aqueous slurry of side-by-side uncrimped staple composite fibers having a latent crimp shrinkage of 70-80% and a length of 20-25 millimeters, and the fiber mat preform has two constraining surfaces. At least one of the latent crimpability by heating the planar array on the condition that the fiber mat preform is in constraining contact with the constraining surface during at least a portion of the heating. A method of forming a nonwoven fabric, wherein the composite fiber contains polyethylene terephthalate and polypropylene terephthalate in respective concentration ratios in the range of 60:40 to 40:60.

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