MXPA00011399A - Process for making load limiting yarn - Google Patents

Abstract

The present invention provides a yarn having a force-displacement profile such that:(a) when the yarn is subjected to an initial stress barrier of from about 0,8 gram/denier to less than or equal to about 1.2 grams/denier, the yarn elongates to less than 5 percent and has an initial modulus in the range from about 30 grams/denier to about 80 grams/denier;(b) upon subjecting the yarn to greater than the initial stress barrier and to less than or equal to about 1.5 grams/denier, the yarn elongates further to at least about 8 percent;and (c) upon subjecting the yarn to greater than 1.5 grams/denier, the modulus increases sharply and the yarn elongates further until the yarn breaks at a tensile strength of at least about 6 grams/denier, wherein the yarn comprises a multiplicity of fibers, all of the fibers have substantially the same force-displacement profile, and are made from polymers having a glass transition temperature in the range from about -40°C to about +70°C. The present invention also provides a process for making block copolymer and a process for making load limiting yarn from the block copolymer. Webbing from the present yarn is useful for seat belts, parachute harnesses and lines, shoulder harnesses, cargo handling, safety nets, trampolines, safety belts or harnesses for workers at high altitudes, military arrestor tapes for slowing aircraft, ski tow lines, and in cordage applications such as for yacht mooring or oil derrick mooring.

Description

PROCESS FOR MANUFACTURING A THREAD OF LOAD LIMITATION BACKGROUND OF THE INVENTION j A safety belt system for a typical vehicle is designed in such a way as to restrict the displacement of an occupant relative to the sitting position of the occupant inside the vehicle when the The vehicle has a sudden, important deceleration. (See US Patent 3,322,163). A typical safety belt has three main parts: retraction belt, the • -or torso belt and lap belt and the performance of each belt can be characterized by its force-displacement curve. The area under the force-displacement curve is known as the energy absorbed by the safety constraint. 15 The safety belts for current vehicles are made of fully stretched polyethylene terephthalate ("PET") fiber that is partially relaxed (2.7%) and has a tenacity of at least 7.5 grams / denier and an elongation at break-up. of 14%. The regulation of The American Government requires that seat belts can withstand loads of up to approximately 27,000 Newtons (6,000 pounds). However, there is a problem with safety belts based on current PET fibers. Impact studies indicate that after the initial impact of the vehicle (for example, to a speed of approximately 56 kilometers / hour) (approximately 35 miles / hour), the occupant tends to move forward from his seated position until the belt is hooked to provide restraining forces. As indicated in Figure 1, the relatively non-elastic belt made from PET fibers exerts a force of at least about 9,000 Newtons (approximately 2,000 pounds) against the occupant in the torso position of the seatbelt causing that the occupant has injuries to the upper chest, rib cage, head, neck and back when the occupant bounces and impacts with the backrest structure of the seat assembly. When a car collides at a speed of approximately 56 kilometers / hour (35 miles / hour), the impact energy to which an average person in the car is subjected is at least 500 Joules in the torso belt. Even though the current PET fiber can absorb the impact energy, damage to the vehicle occupant continues to occur due to the undesirable force-displacement curve. In 70 milliseconds a passenger of average size will experience high forces of up to approximately 9,000 Newtons (2,000 pounds) as shown in Figure 1. In order to absorb the energy of the impact and to reduce the load of the seat belt against the occupant of the vehicle, U.S. Patent No. 3,550,957 discloses a shoulder harness having double sewn sections of the fabric arranged above the occupant's shoulder such that the seam allows the fabric to elongate from an initial length to a final length of a controlled speed under the influence of a predetermined restriction force. However, sewn sections do not provide the desirable amount of energy abstractions, do not provide a uniform response, and can not be reused in multiple accidents. See also US Pat. No. 4,138,157. U.S. Patent 3,530,904 discloses a woven fabric constructed by weaving two types of yarns having relatively different physical properties and demonstrating energy absorption capacity. U.S. Patent Nos. 3,296,062; 3,464,459; 3,756,288; 3,823,748; 3,872,895; 3,926,227; 4,228,829; 5,376,440; and Japanese Patent 4-257336 further disclose fabrics constructed of various types of warp yarns having different tenacity and different elongations at break. DE 19513259 A1 discloses fabrics constructed of short warp yarns that absorb the initial stress load acting on the fabric and also longer warp yarns that absorb the subsequent stress load * acting on said fabric.

Those skilled in the art have recognized deficiencies in the use of at least two different types of yarn in accordance with what is taught by the references just mentioned. U.S. Patent 4,710,423 and Kokai Patent Publication 298209 published December 1, 1989 ("Publication 298209") teach that when at least two different types of wire are used, energy absorption occurs in a staggered manner and therefore the fabric does not absorb energy in a continuous and smooth way. Therefore, after one type of warps has absorbed a portion of the impact energy, and before another type of warps absorbs another portion of the impact energy, the human body is exposed to an undesirable shock. UK Patent 947,661 discloses a safety belt having an elongation greater than or equal to 33% when it is subjected to at least 70% of the breaking load. This reference does not teach or suggest the present thread of load limitation. U.S. Patent 3,486,791 discloses energy absorbing devices such as a coiled device that separates a relaxed section of the belt from the taut body restraining section by a clamping device that deforms under a predetermined restraining force to gradually feed the section relaxed in such a way that the stretched section lengthens allowing the restricted body to move at a controlled speed. The reference also describes a device that anchors the belt to the vehicle through an anchor member fixed on the belt and integrated into a solid plastic energy absorber. These types of mechanical devices are expensive, can not be reused, provide unsatisfactory energy absorption, and are difficult to control. An improvement compared to the aforementioned devices is presented in U.S. Patent 5,547,143 which discloses a load absorption retractor comprising: a rotating reel, a seat belt fabric fixed on the spool; and at least one movable bushing responsive to loads generated during a crash situation, for the deformation of a part of the spool and thereby dissipate a predetermined amount of energy. This type of mechanical device is integrated with a specific amount of load limit and energy absorption for occupants of a certain size, and can not be adjusted to the needs of occupants of different sizes in the real transport scenario. Furthermore, this type of mechanical device can not be reused to limit the load in several accidents since the spool is permanently deformed in the first collision of the vehicle. U.S. Patent 4,710,423 and Publication 298209 disclose fabrics consisting of relaxed polyethylene terephthalate ("PET") yarns having a tenacity of at least 4 grams / denier and a final elongation of 50% a • 80%. Due to the inherent physical properties of PET yarn (eg, glass transition temperature = 75 ° C), the examples of US Patent 4,710,423 and Publication 298209 show that, at an elongation of 5%, the load It has already reached more than approximately 6,700 Newtons (1,500 pounds). Damage to the occupant caused by the • 10 safety belt still exists and therefore the belt material must be modified. Examples of these two patents also show that if the PET yarn is over-relaxed, the yarn tenacity drops to 2.3 grams / denier. 15 Kokai Patent Publication 90717 published April 4, 1995 discloses a high strength tissue-based polybutylene terephthalate ("PBT") homopolymer fiber ("PBT"). • energy absorption. The tenacity of the fiber is greater than 5.8 grams / denier, its elongation at break is greater that 18.0%, and the effort at an elongation of 10% is less than 3.0 grams / denier. However, this reference does not present PBT fiber that demonstrates the initial effort requirement that engages the seatbelt to protect the occupant and the barrier control device. initial effort. A barrier of initial low effort of a Thread results in a low deflection force point of the finished safety belt which allows excessive displacement of the occupant and causes injuries • severe. It would be desirable to have an improved energy absorption safety belt that has a smoother performance than the performance of the known sewn fabric approach or the known use of at least two different fibers, which can be reused in several accidents as opposed to the W 10 device and known mechanical restraint, and that also solves the ability to control the initial stress barrier and the impact energy absorption of vehicle occupants of different sizes. The present inventors in the patent application North American commonly assigned Serial No. 08 / 788,895 filed April 18, 1997 and the authorized US Patent Application Serial No. 08 / 819,931 filed • On March 18, 1997, they responded to the previous need. See also, T. Murphy, "Buckling Up for the Future "(using the safety belt for the future) ARD's Auto World, 95 (1997) COMPENDIUM OF THE INVENTION The present invention also responds to the prior art need by providing a limiting yarn of loading, a process for making the thread of load limitation, and a fabric made from the load limiting yarn. The fabric, if used as a safety belt to restrain an occupant, demonstrates energy absorption and load limiting performance. This type of load limiting safety belt comprises a yarn having a force-displacement profile characterized by the following: (a) when the yarn is subjected to an initial stress barrier of about 0.8 gram / denier to a ^ 10 level less than or equal to about 1.2 grams / denier, the yarn is stretched to less than 5% and has an initial modulus within a range of about 30 grams / denier to about 80 grams / denier; (b) by subjecting the wire to an effort greater than the barrier of Initial stress and at an effort less than or equal to about 1.5 grams / denier, the yarn is further lengthened to at least about 8%; and • (c) when submitting the yarn to an effort greater than 1.5 grams / denier, the modulus is strongly increased and the yarn is further stretched until the yarn breaks at a tensile strength of at least about 6 grams / denier, where the yarn comprises several fibers, all fibers have substantially the same force-displacement profile, and are made from polymers that have a glass transition temperature within a range from about -40 ° C to about + 70 ° C. The term "modules" as used herein refers to the slope of the force-displacement curve. • Figure 2 illustrates the force-displacement profile of the example of the present invention. The initial stress barrier is indicated as ISB in Figure 2. The present tissue formed by this type of yarn is useful since the present fabric has a better absorption of impact energy and a smoother performance than in the case • 10 of the prior art sewing fabric approach or the known use of at least two different fibers, can be reused unlike the known mechanical mechanism, and also solves the problem of the ability to control the initial stress barrier and the energy absorption of impact. The present invention also provides a process for manufacturing a load limiting yarn comprising the • manufacture of a block copolymer and then the spinning of the block copolymer in a yarn. The present invention to make a block copolymer useful in the charge limiting yarn of the present invention occurs in a two screw extruder comprising the steps of: (A) advancing the aromatic polyester function towards an injection position in the extruder of double screw in where the aromatic polyester has: (I) an intrinsic viscosity which is measured in a 60/40 weight mixture of phenol and tetrachloroethane and is at least about 0.6 deciliters / gram and (II) a Newtonian melt viscosity which is calculated to be about 7,000 poise at a temperature of 280 ° C; (B) injecting a lactone monomer into the melted aromatic polyester from step (A); (C) dispersing the injected lactone monomer in the aromatic polymer melt in such a way that a uniform mixture is formed in less than about 30 seconds; and (D) reacting the uniform mixture resulting from step (C) at a temperature from about 250 ° C to about 280 ° C to form a block copolymer. All steps (A) to (D) occur in less than about four minutes residence time in the twin screw extruder. The process of the present invention is advantageous because an initial high IV aromatic polyester can be employed and the short reaction time at high temperature results in a block copolymer with minimal transesterification, high melting point, and high viscosity of fusion. Preferably, the block copolymer has a melting point of at least about 220 ° C. Preferably, the block copolymer melt is then devolatilized in step (E) in the twin screw extruder to remove the residual lactone monomer. Preferably, after devolatilization, ultraviolet ray absorbers, antioxidants, pigments, and other additives are then injected into step (F) and dispersed in the copolymer melt in the twin screw extruder. The block copolymer is then advanced from the twin screw extruder to a fiber spinning equipment. The process of the present invention for making fibers from the block copolymer comprises the steps of: (G) from the twin-screw extruder, introducing the melt of block copolymers at a temperature from about 240 ° C to about 280 °. C in a spinning vessel and extruding filaments from the spinning vessel; (H) passing the extruded filaments through a heated sleeve having a temperature from about 200 ° C to about 300 ° C; (I) cooling the filaments with ambient air wherein the air flows perpendicular to the direction of the filament at a flow rate of at least about 0.1 meter per second; (J) applying a spin finish to the cooled filaments; (K) pick up the filaments to form a thread in a first cylinder; (L) passes the yarn to a second cylinder having a temperature greater than the glass transition temperature of the yarn unless the crystallization temperature of the yarn; (M) stretching the yarn between said second cylinder and stretching cylinders on a heated shoe or in a stretch point locator positioned between said first cylinder and stretching cylinders and having a • 10 temperature from about 180 ° C to about 350 ° C and then pick up the drawn yarn in said stretching cylinders having a temperature of about 140 ° C to about 200 ° C; (N) relax the drawn yarn between said cylinders of and a final cylinder in such a way that the relaxed yarn has a shrinkage of about 7% to about 20%; • (O) cool the relaxed yarn in the final cylinder device at room temperature; and 20 (P) wind the cooled yarn. The aforementioned process for making a block copolymer in a twin-screw extruder and for spinning a load limiting yarn can be carried out in a continuous process from the block copolymerization to the final yarn wound or in a discontinuous process in where the block copolymer is prepared in the twin screw extruder and cut and the pieces of copolymers are then spun from a single screw extruder in • one thread of load limitation. Other advantages of the present invention will be apparent from the following description, from the accompanying drawings and from the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates the performance (with load as a function of time 10) of a polyethylene terephthalate homopolymer seat belt in the torso position in a vehicle collision. Figure 2 illustrates a stress-strain curve of the yarn of the present invention. Figure 3 illustrates a double screw extruder configuration useful in the process of the present invention. Figure 4 illustrates the present fiber-stretch-relax process. Figure 5 illustrates the performance (load-dependent 20 time) of the load-limiting safety belt of the present invention in the torso position in a vehicle collision. DETAILED DESCRIPTION OF THE INVENTION The present yarn has the following profile- force-displacement. (a) When the yarn is subjected to an initial stress barrier of approximately 0.8 gram / denier at an effort and less than or equal to approximately 1.2 grams / denier, the • Yarn is lengthened to less than 5% and preferably less than 5 3%. The yarn has an initial modulus within a range of about 30 grams / denier to about 80 grams / denier, and the preferred initial modulus is within a range of about 40 grams / denier to about 60 grams / denier. The high initial module of The yarn and the height of the initial stress barrier are required to engage the seat belt and to ensure that all collision energy of the occupant will be absorbed under the subsequent load limitation portion of the force-displacement curve. 15 (b) When the yarn is subjected to an effort greater than the initial stress barrier and an effort less than or equal to approximately 1.5 grams / denier, the yarn is stretched • additionally up to at least about 8%. Preferably, the yarn is stretched to at least approximately 10%. This portion of the force-displacement curve is the load limit portion of the wire that absorbs the collision energy and prevents the passenger from experiencing excessive loads, (c). When submitting the thread to an effort greater than 1.5 grams / denier, the module is strongly increased and the thread it is further extended until the yarn breaks at a tensile strength of at least about 6 grams / denier. The yarn comprises several fibers and all the fibers have substantially the same force-displacement profile. The term "various fibers" as used herein refers to at least 100 filaments that are employed for each safety belt thread tip. In a seatbelt fabric comprising at least 300 tips of the aforementioned thread, the load in the passenger's torso position can be reduced to approximately 2,000 Newtons (450 pounds) even in the case of a collision of approximately 56 kilometers. / hour (35 miles / hour). The reduced force then minimizes or eliminates potential damage to the vehicle occupant. The yarn is made from a polymer having a glass transition temperature within a range from about -40 ° C to about + 70 ° C, preferably from about -20 ° C to about + 60 ° C, and more preferably from about + 35 ° C to about + 55 ° C. The polymer can be a homopolymer, random copolymer, block copolymer, block copolymer, or segmented block copolymer. Examples of preferred homopolymers include polytrimethylene terephthalate; polyisobutylene terephthalate; as well as Long chain alkylene terephthalates and naphthalate polymers. Examples of preferred random copolyesters include copolyesters which, in addition to the ethylene terephthalate unit, contain components such as ethylene adipate, ethylene sebacate, or other long chain alkylene terephthalate units. This component is present in an amount greater than 10%. Examples of preferred block copolymers include structure of two blocks, three blocks, and segmented blocks. The block copolymers comprise at least one hard crystalline aromatic polyester block and at least one soft amorphous aliphatic polyester block. Crystalline aromatic polyester includes homopolymers such as polyethylene terephthalate ("PET"); polytrimethylene terephthalate; polybutylene terephthalate; polyisobutylene terephthalate; poly (2,2-dimethylpropylene terephthalate); poly [bis- (hydroxymethyl) cyclohexene terephthalate]; polyethylene naphthalate ("PEN"); polybutylene naphthalate; poly [bis- (hydroxymethyl) cyclohexene naphthalate]; other polyalkylene or polycycloalkylene naphthalates, and mixed polyesters which, in addition to the ethylene terephthalate unit, contain components such as ethylene isophthalate; ethylene adipate; ethylene sebacate; 1, 4-cyclohexylenedimethylene terephthalate; or other units of long chain alkylene terephthalate. Commercially available aromatic polyesters can also be used. A mixture of aromatic polyesters can also be used. The most preferred aromatic polyesters include PET and PEN. Preferably, the amorphous aliphatic polyester block is made from a lactone monomer. Preferred lactone monomers include epsilon-caprolactone, propiolactone, butyrolactone, valerolactone, and higher cyclic lactones. The most preferred lactone monomer is epsilon-caprolactone. Commercially available lactone monomers may also be employed. Two or more types of lactones can be used simultaneously. Preferably, the aromatic polyester has: (I) an intrinsic viscosity which is measured in a mixture of 60/40 by weight of phenol and tetrachloroethane at a temperature of 25 ° C and is at least about 0.6 deciliters / gram and (II) a Newtonian melt viscosity which is calculated to be at least about 7,000 poise at 280 ° C. The intrinsic viscosities, as measured in a 60/40 weight mixture of phenol and tetrachloroethane, of the polyesters Preferred aromatics are about 0.8 for PET and about 0.6 for PEN. The most preferred intrinsic viscosity for PET is 0.9 and for PEN it is 0.7. The Newtonian melt viscosity of PET (with a intrinsic viscosity = 1) is calculated at approximately 16,400 poise at 280 ° C and the Newtonian melt viscosity of PEN (with intrinsic viscosity = 1) is greater than the melt viscosity of PET. For use in load limiting safety belts, the PET-polycaprolactone block copolymer can have a polycaprolactone concentration of preferably from about 10 to about 30% by weight. In the block copolymer, the concentration of polycaprolactone may vary in order to achieve the desired initial stress barrier and absorption of impact energy with load limiting performance. The process of the present invention for making a block copolymer useful in the present charge limiting yarn occurs in a twin-screw extruder and comprises the steps of: (A) advancing an aromatic polyester melt to an injection position in a twin screw extruder wherein the aromatic polyester melt has (I) an intrinsic viscosity which is measured in a 60/40 weight mixture of phenol and tetrachloroethane and which is at least about 0.6 deciliters / gram and (II) a Newtonian melt viscosity that is calculated at at least about 7,000 poise at 280 ° C; (B) injection of lactone monomer into the polyester melted aromatic from step (A); (C) dispersion of the lactone monomer injected into the aromatic polymer melt in such a way as to form a mixture • uniform in less than about 30 seconds; and (D) reacting the uniform mixture resulting from step (C) at a temperature from about 250 ° C to about 280 ° C to form a block copolymer. All steps (A) to (D) occur in a residence time of less than about four minutes in the extruder of • 10 double screws. Step (A) for making the block copolymer in a twin-screw extruder comprises advancing the aromatic polyester melt to an injection position. The aromatic polyester is added to the twin screw extruder.

The aromatic polyester can be melted and then fed by a melt introduction pump to a twin screw extruder or the aromatic polyester can be fed in the form of nodules fed to a "compensation" feeder to the twin screw extruder and then melted in the double screw extruder. As known to those skilled in the art, a compensating feeder has a hopper filled with nodules and the feed rate is controlled by the weight loss of the nodules from the hopper. If the polyester melt aromatic from a reactor is used as the material Initial, narrow gear transport elements can be used to transport the downstream melt. If aromatic polyester nodules are used as initial material, • transport element is preferably assembled from open gear, open to closed and closed under the feed position in the twin screw extruder to melt the nodules and to transport the downstream melt to the injection position. We have found that by using a double extruder • 10 screws, mixing and reaction of the aromatic polyester melt with the lactone monomer having a drastic viscosity difference is feasible. Useful double screw extruders are available commercially; however, the mixing elements and the arrangement sequence of The elements in the twin screw extruder that are required for the present invention are critical factors and are described below. The double extruders • Preferred screws are twin-screw extruders. Figure 3 illustrates one of the processes of extrusion of double geared screws employed in the present invention. A single screw extruder, as indicated in US Patent 4,045,401 is not useful in the present invention because a single screw extruder does not provide rapid mixing, residence time, distribution of residence times, the agitation of fusion, and process control that are required for the present invention. The initial extrusion temperature exceeds the melting point (in accordance with that measured by Perkin-Elmer Differential Scanning Calorimeter (DSC) from the endotherm maxima resulting from the scanning of a 2 milligram sample at a temperature of 20 ° C per minute) of the aromatic polyester used. The melting points of the preferred aromatic polyesters are 250 ° C for PET and 266 ° C for PEN. The temperature in the preferred initial extrusion zone is at least about 30 ° C above the melting point of aromatic polyester. Thus, the preferred extrusion temperature for PET is at least about 280 ° C while the preferred initial extrusion temperature for P EN is at least about 296 ° C. Step (B) for making the block polymer comprises the injection of lactone monomer into the melted aromatic polyester of step (A). Preferably, a piston pump is used to inject the lactone monomer at a constant rate into the aromatic polyester function. Preferably, the lactone monomer is premixed with catalysts at room temperature. Commercially available catalysts can be used. The preferred catalysts are organometallic based on metals such as lithium, sodium, potassium, rubidium, cesium, magnesium, salts of inorganic acids, oxides of salts of organic acids and alkoxides of calcium, barium, strontium, zinc, aluminum, titanium, cobalt, germanium, tin, lead, antimony, 5 arsenic , cerium, boron, cadmium, and manganese; and its organometallic complexes. More preferred catalysts are salts of organic acid and organometallic compounds of tin, aluminum and titanium. The most preferred catalysts are tin diacylate, tin tetraacrylate, dibutyltin oxide d, dibutyl tin dilaurate, tin octonate, tin tetraacetate, triisobutylaluminum, aluminum acetylacetonate, aluminum isopropoxide, aluminum carboxylates, tetrabutyl titanium, germanium dioxide. , antimony trioxide, profirin complexes and phthalocyanine of these metal ions. Two or more types of catalysts can be used in parallel. Preferably, the amount of catalyst employed is from about 0.1 to about 0.2% by weight based on the combined weight of aromatic polyester and monomer of lactone. Step (C) for preparing the block copolymer comprises the dispersion of the lactone monomer injected into the aromatic polymer melt in such a way that a uniform mixture is formed in less than about thirty seconds and Preferably, in less than about twenty seconds. The The expression "uniform mixture" as used herein refers to a regulated distribution of the lactone monomer in the aromatic polyester melt. Preferably, distribution comb mixers are used to disperse the lactone monomer injected into the high melt viscosity aromatic polyester melt. This rapid uniform mixing formation results in a uniform ring opening polymerization of lactone, uniform block copolymer product, and stable process downstream. Preferably, at least one direct distributive gearing comb mixer, at least one central distributive gearing comb mixer, and at least one reverse distributive gearing comb mixer are employed to achieve the desired mixing. Step (D) for making the block copolymer comprises the reaction of the uniform mixture resulting from step (C) at a temperature from about 250 ° C to about 280 ° C to form a block copolymer in less than about four minutes . The mixture is further advanced downstream in a reaction zone where there are turbulence devices, mixers and transport element. The turbulence devices are used to continuously stir the melt, increase the extruder volume without sacrificing the yield, and control the reaction time. The group of The hydroxyl end of the aromatic polyester initiates a ring opening polymerization of lactone monomer under catalytic conditions to form a lactone block at the end of the aromatic polyester. The fusion is constantly stirred by the turbulence devices and mixing elements to homogenize the reaction. This short reaction time minimizes transesterification while ensuring a complete reaction which means the polymerization of the lactone monomer to form the block at the end of the aromatic polyester chain and the complete consumption of the injected lactone monomer. To determine the residence time and residence distribution time, we added colored nodules that served as markers for the aromatic polyester nodules. The term "residence time" means the period of time beginning from the addition of the colored nodules until the appearance of the strongest color. The term "residence distribution time" means the time range from the appearance of the color and ending with the disappearance of the color. As the residence distribution time decreases, the uniformity of the product increases. The residence distribution time is preferably less than about three minutes and especially less than about one minute. Preferably, the degree of transesterification between the aromatic polyester and lactone blocks is less than 5% by weight of the combined weight of the material. Preferably, the block copolymer melt is then devolatilized in step (E) in vacuum in the twin screw extruder to remove the residual lactone monomer. The devolatilization element allows the formation of a thin polymer melt film and a high surface area for the effective removal of volatile substances. Preferably, after devolatilization, ultraviolet radiation absorbers, antioxidants, pigments and other additives are then injected in step (F) and dispersed in the copolymer melt in the twin screw extruder through a piston pump or a gear pump at a constant rate. The direct distribution comb mixers are used to homogenize the additives in the copolymer. The melt in the temperature range from about 240 ° C to about 280 ° C is then transported downstream to a melt introduction pump for spinning the fibers. The preferred ultraviolet absorbers are benzophenone-based stabilizers, benzotriazoles, triazines, and oxanilides. The most preferred ultraviolet ray absorbers are 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-hexyloxyphenol.; 2- [4,6-bis (2,4-dimethylphenyl) -1,3,5-triazin-2-yl] -5-octyloxyphenol; 2- (2H-benzotriazole-2- il) -p-cresol; 2- (2H-benzotriazol-2-yl) -4,6-bis (1-methyl-1-phenylethyl) phenol; 2-ethoxy-2'-ethyloxanilide; 5-tert-butyl-2-ethoxy-2'-ethyloxyanilide; propandioic acid; ((4-methoxyphenyl) -methylene) -; and bis (1, 2, 2, 6, 6-pentamethyl-4- 5 piperidinyl) ester. Two or more types of stabilizers can be used in parallel. Preferably, the amount of ultraviolet radiation absorber that is employed is from about 0.1 to about 2% by weight based on the combined weight of the aromatic polyester and monomer of lactone. Preferred antioxidants are additives based on hindered phenols, hindered benzoates, hindered amines, and phosphites / phosphonites. The most preferred antioxidants are tetrakis (methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate)) methane; bis (3- (3'-tert-butyl-4'-hydroxy-5'-methylphenyl) propionate) of triethylene glycol; 1,6-Hexandiamine, N, N'-bis (2, 2, 6,6-tetramethyl-4'-piperidinyl) - polymer, with morpholine-2,4,6-trichloro-1,3,5-triazine; and tris (2,4-di-tert-butylphenyl) phosphite. Two or more types of additive can be used. Preferably, the amount of antioxidant employed is from about 0.1 to about 1% by weight based on the combined weight of the aromatic polyester and the lactone monomer. The block copolymer is then taken from the extruder double screws to the fiber spinning equipment. He The present process for making a charge limiting yarn from the block copolymer comprises the steps of: (G) from the twin screw extruder and through a melt measuring pump, introduce the block copolymer melt at a temperature from about 240 ° C to about 280 ° C in a spinning vessel and extrude the filaments from from the spinning vessel equipped with a spinneret; (H) passing the extruded filaments through a heated sleeve having a temperature from about 200 ° C to about 300 ° C; (I) cooling the filaments with ambient air wherein the air flows perpendicular to the direction of the filament and at a flow rate of at least about 0.1 meter per second; (J) applying a spin finish to the cooled filaments; (K) collecting the filaments to form a yarn in a first drum; (L) passing the yarn to a second drum having a temperature higher than the glass transition temperature of the yarn unless the temperature of crystallization of the yarn; (M) pulling the thread between said second drum and drawing drums in a heated shoe or in a stretch point locator placed between said second drum and drums of stretched and having a temperature from about 180 ° C to about 350 ° C and then annealing the drawn yarn in said drawing drums having a temperature from about 140 ° C to about 200 ° C; (N) relaxing the drawn yarn between said drawing drums and a final drum such that the relaxed yarn has a shrinkage of about 7% to about 20%; (P) cool the relaxed yarn in the final drum set at room temperature; and (Q) wind the cooled yarn. The aforementioned process for making the block copolymer in a twin-screw extruder and the spinning of the load limiting yarn can be carried out in a continuous process from the block copolymerization to the final wound yarn or it can be processed in a process discontinuous wherein the block copolymer is prepared in the twin screw extruder and cut and the copolymer cuts are then spun from a single screw extruder in a load limiting wire. Figure 4 illustrates the process of the present invention for manufacturing a load limiting yarn with a specific type of stress-strain curve (Figure 2) The process consists of the block copolymerization in the twin screw extruder, the spinning of the merger, the filament cooling, stretching, relaxing and winding the yarn. In step (G), which is the first step for making a charge limiting wire from the block copolymer, melting at a temperature of about 240 ° C to about 280 ° C is fed through a metering pump into a spinning container consisting of filtering screens and a row. Preferably, the polymer throughput in the spinneret is within a range of about 1.5 grams / hole / minute to about 3.5 grams / hole / minute and the spinning temperature is within a range of about 240 ° C. to about 280 ° C. Preferably, the melt viscosity of the PET-polycaprolactone copolymer under these spinning conditions, e.g., spinning and shearing temperature, is from about 2,000 to about 4,000 poise. The filaments are extruded from the spinning vessel. In steps (H) and (I), the extruded filaments pass through a heated sleeve having a temperature from about 200 ° C to about 300 ° C and are then cooled by ambient air flowing perpendicular to the direction of the filament at a flow rate of at least about 0.1 meter / second. The ambient air has a temperature of about 10 ° C to about 30 ° C. The proper temperature of the heated sleeve and the proper air flow rate are important to achieve uniformity of • filament and thread that is required. The yarn uniformity is measured by the uster method that indicates the denier consistency of the yarn. Filament uniformity is measured by a radial birefringence method that indicates the degree of molecular orientation on both the surface and the core of the filaments. Prior to harvesting, a spin finish is applied in step (J) onto the cooled filaments through a finishing applicator. Preferably, the applied spin finish is based on a water-soluble low molecular weight polymer that can be removed efficiently by dissolving it in water. In step (K), the cooled filaments are collected by a first drum to obtain a yarn in the spun condition with a low molecular orientation and minimal crystallinity. The • "Low molecular orientation" expression, as used herein, preferably means that radial birefringence is less than about 0.001. The term "minimal crystallinity", as used herein, preferably means that the crystallinity is less than about 5%. In step (I), the yarn is then fed to a second drum having a temperature higher than the transition temperature to thread glass ("Tg") unless the temperature of crystallization of the thread ("Te"). The glass transition temperature of a PET-polycaprolactone copolymer ranges from about 35 ° C to about 55 ° C, based on the weight percentage of epsilon-caprolactone in the polymer and block transesterification. The crystallization temperature of a PET-polycaprolactone copolymer ranges from about 100 ° C to about 170 ° C, depending on the weight percentage of epsilon-caprolactone in the polymer and the degree of transesterification. The purpose of heating is to preheat the yarn. In step (M), the preheated yarn is drawn between the second drum and draw drums in a heated shoe or in a stretch point locator positioned between the second drum and draw drum and has a temperature of about 180 ° C at about 350 ° C and the drawn yarn is then annealed in the stretching drums having a temperature from about 140 ° C to about 200 ° C. The purpose of the heated shoe or stretch point locator is to further heat the thread and locate the thread stretch. The hot media in the stretch point locator can be air or steam. The draw drums have a temperature between about 140 ° C and about 200 ° C and are used to promote crystallization and Annealing of the thread. Preferably, the yarn is stretched at a stretch ratio of at least 6: 1. The time for annealing the drawn yarn is less than • approximately one second. 5 In step (N), the drawn yarn is relaxed between the stretching drums and a final drum with a controlled shrinkage established by the speed difference of the drums and the temperature of the stretching drums from which it relaxes the thread. From Preferably, the degree of shrinkage lies within a range of between about 7% and about 20% to provide the yarn with a desired stress-strain curve. The final drum is adjusted to room temperature. In steps (0) and (P), the thread relaxed is cooled and wound on a reel adjusted to room temperature and to the speed of the final drum. Safety belts are frequently woven with a warp yarn of approximately 1000 to approximately 1500 denier and a breaking strength of at least approximately 5 grams / denier and a weft yarn with a denier of about 200 to about 900 and a breaking strength of at least about 5 grams / denier. The fabric conditions are selected in such a way that the safety belt retains the stress / strain properties of the yarn and in such a way that maintains the resistance of the fabric. Our results indicate that the 2x2 cross-over tissue pattern most commonly used can be used successfully for the preparation of • safety belts with load limitation. The seatbelt fabric is dyed in a thermosol kit at a temperature between about 100 ° C and about 180 ° C. Car collision tests at a speed of about 56 kilometers per hour (35 miles per hour) of this type of 10 load limitation safety belts show that the force against occupants is reduced from 3.6 KN (800 lbs) - 7.2 KN (1600 lbs) and injury criteria are minimized. The fabric of the present invention provides the desired characteristics of load limitation in the absence of a fastening device as taught in U.S. Patent No. 3,486,791; in the absence of sewing as taught in U.S. Patent No. 3,550,957; and in the absence of a mechanical energy absorption device such as the constant force retractor taught in , North American Patent No. 5,547,143. The fabric and yarn of the present invention provide the desired load limiting characteristics and are made of a material other than the PBT homopolymer taught in publication 90717. The fabric of the present invention offers the desired characteristics of load limitation by the use of warp yarns that have substantially the same force-displacement profile instead of the various strength profiles - warp yarn displacement • taught in North American patents 3,872,895; 5,288,829; and 5,376,440. The fabric of the present invention provides the desired load limiting characteristics and is made of polymer other than PET homopolymer taught in U.S. Patent 4,710,423 and Publication 298209. • The fabric of the present invention is useful for safety belts , harness and chords for parachutes, shoulder harnesses, safety nets, cargo handling, trampolines, safety belts or harnesses for workers who work in high places, military detention tapes for reduce the speed of aircraft, skid lines and in rope applications such as for mooring yachts or for mooring towers over oil wells. TEST METHODS 20 In the following examples, the reduced specific viscosity was determined as follows. The viscosity of the solution and the viscosity of the solvent were measured and the specific viscosity was calculated by (solution viscosity - solvent viscosity) / (viscosity of solvent).

The reduced specific viscosity was calculated from specific viscosity / solution concentration. The intrinsic viscosity of polymer was determined by plotting the reduced specific viscosity of polymer solution versus solution concentration in a mixed solvent of 60 parts of phenol and 40 parts of tetrachloroethane at 25 ° C. The intersection was the intrinsic viscosity of the polymer. It is understood that the intrinsic viscosity is expressed in units of deciliters per gram (or (dl / g)) even when such units are not indicated. The thermal properties were measured using a differential scanning calorimetry device 7 from Perkin Elmer using a sample size of polymer cuts of approximately 5 milligrams, heating the sample to 285 ° C at a rate of 5 ° C / minute, maintaining the sample at a temperature of 285 ° C for 2 minutes, and cooling the sample at 30 ° C at a rate of 10 ° C / minute. The peak temperature of the endotherm in the thermal scan was the melting point of a polymer and the peak exotherm temperature in the cooling scan was the crystallization temperature of a polymer. The glass transition temperature of a polymer was the second order thermal transition temperature during heating and cooling scans. For the preferred block copolymer yarn, the Newtonian melt viscosity for the initial PET of the example of the present invention was calculated at about 7,000 poise at 280 ° C with basis Andizej Ziabicki "Effeets of • Molecular Weight on Melt Spinning and Mechanical Properties 5 of High Performance Poly (ethylene Terephthalate) Fibers, "(Effects of Molecular Weight on Fusion Spinning and on the Mechanical Properties of High Performance Polyethylene Terephthalate Fibers), Textile Res J. 66 (11), 705-712 (1996) and A. Dutta, "Identifying Critical Process • 10 Variables in poly (ethylene Terephthalate) Melt Spinning " (Identification of Critical Process Variables in the Polyethylene Terephthalate Fusion Yarn), Textile Res. J. 54, -42 (1984). The Newtonian melt viscosity refers to the melt viscosity at a zero shear stress. 15 The melt viscosity of block copolymer under various spinning conditions was extrapolated from fusion rheology data obtained from capillary rheometer • Kayeness Galaxy V with capillary die L / D = 30: 1 using shear forces located from 50 / sec. to 998 / sec. The samples were dried at a temperature of 160 ° C for 16 hours in vacuum before measurement. 15 grams of sample were packed in the rheometer and the mixture was allowed to reach thermal equilibrium for 6 minutes before starting melt viscosity measurements. Experiments were made at different temperatures with an effort constant shear in a range of shear stresses of 50 sec-1, 100 sec "1, 200 sec" 1, 499 sec "1, and 998 sec" 1 and for periods of up to 20 minutes. No corrections were made for the final effects in such a way that the values are apparent melt viscosities. The radial birefringence was determined by the use of an Ausjena interference microscope to measure the radial structure through a correct measurement of the refractive index profiles of the fiber. An oil with a refractive index of 1,300 to 1,800 was used. A regular model was used to calculate the refractive index profile based on three considerations 1) the fiber is perfectly symmetric around its center, 2) the refractive index profile varies smoothly, and 3) the fiber is round . Tension properties were measured in an Instron machine equipped with a pneumatic rope and wire handles that hold the threads in a length of 25.4 cm (10 inches). The yarn in the state in which it was wound was then pulled at a deformation rate of about 25 centimeter / minute (10 inches / minute) under standard conditions (23 ± 2 ° C, relative humidity 50% ± 5%) and The data was recorded by a pressure indicator. From these data, the stress-deformation curves were obtained. The tenacity was the breaking resistance (in grams) divided by the yarn denier.

Shrinkage was defined as a longitudinal shrinkage of a yarn when exposed to an elevated temperature. Here, the shrinkage was calculated based on the • Stretch roller speed difference and last 5 roller divided by the speed of the stretch rollers. EXAMPLE OF CONFORMITY WITH THE PRESENT INVENTION With reference to Figure 3, dried PET pellets (intrinsic viscosity = 0.9, calculated MV = 15,310 poise a • 10 280 ° C were fed by a Ktron "compensation" feeder to a counter rotating twin screw extruder 10 (diameter = 27 millimeters, length = 1296 millimeters, screw = 150 revolutions per minute) at the feed point 12 at a rate of 5.81 kg / hour (12.8 lbs / hour). In the direction of arrow 14, the nodes were transported by open gear elements 16 downstream and began to melt into the adjacent gear elements 18 in the first zone 20 and in the second zone 22. The fusion was then transported to a third zone 24 in a compression element 26 that acted as a dynamic seal at the end of the feed zone and provided strong compression and reduced the return flow of the melt of polymer and injected materials. The first feeding area was not heated. The temperature of the second zone and the third zone was set at 290 ° C. The pre-mixed e-caprolactone and the catalyst (tin octonate, 0.075% by weight PET-polycaprolactone) were injected into the extruder through a piston pump at an injection point 28 to a regime of approximately 1 kilogram / hour (2.2 pounds / hour). The injected materials were mixed with the PET fusion in a back-and-forth movement by two direct meshing distribution combiners 30 and 32 (30 millimeters) two neutral mesh combing mixers (30 millimeters) 34 and 36, and a reciprocating gear mixer 38 of gear distribution (30 millimeters) assembled in the region of the injection point 28. A uniform mixture was obtained in 30 seconds and this mixture was transported to the area of reaction. The temperature of the fourth zone 40 was set at 280 ° C. The temperature of reaction zones through zones 42, 44, 46 and 48 was set at 262 ° C. In this zone, in the presence of tin octonate, the chain extension of PET by ring-opening polymerization of e-caprolactone was initiated by the hydroxyl end of PET. The reaction zone consisted of two turbulence forming devices 50 and 52 (110 millimeters) that provided a high percentage extrusion volume, followed by a neutral mixer 54 which homogenized the reaction, and two turbulence forming devices 56 and 58 (30 millimeters), which provided a longer contact time for chain extension. This screw pattern allowed • finishing the reaction in reaction time or residence time of 4 minutes and the melt was continuously stirred during the reaction. The polymerized melt was brought to a devolatilization zone 60 where the vacuum was set at -950 mbar. The amount of unreacted e-caprolactone that is removed was 0.36% by weight of the e-caprolactone injected. The intrinsic viscosity of the PET-polycaprolactone copolymer (15%) was 0.97. Transesterification between blocks of PET and caprolactone was less than 5%. The glass transition temperature of the copolymer was 45 ° C, and the The melt temperature of the copolymer was 231 ° C. With reference to Figure 4, the melt produced by the extrusion process in double reactive screws was • fed to a spinning container 110 by a metering pump at a rate of approximately 7 kilograms / hour (15 pounds / hour). The melting temperature was controlled at a temperature of 260 ° C. The pressure at the end of the extruder was 49.3 kg / cm2 (700 pounds per square inch) and the pressure in the spinning container was 89.51 kg / cm2 (1270 pounds) per square inch). 25 The spinning container contained three mesh screens layer and a row with 50 round holes with a diameter dimension of approximately 0.053 centimeters (0.021 inches) and a length of approximately 0.183 centimeters (0.072 inches). The polymer production was 2.27 grams / hole / minute with a shear rate of 2.150 sec "1. The melt viscosity of PET / PCL 15% in the spinning condition (shear rate = 2.150 sec" 1 and the melting temperature = 260 ° C was about 2,800 poise.The extruded filaments were passed through a heated sleeve 112 set at 280 ° C and were cooled by air flow perpendicular to the yarn in the state in which it was spun a flow velocity of 0.13 meter / second A water-soluble spin finish was applied at 114 to the yarn, and the yarn was collected in a drum 116 at a speed of 270 meters / minute to form a yarn in the state at The yarn in the state in which it was spun had a radial birefringence equal to 0.001 and a denier of 3780. The yarn in the state in which it was spun was then fed to a roller 118 heated to a temperature of 60 °. C at the speed of 275 meter s / minutes and stretched 6.7: 1 in a hot shoe 120 with a temperature of 218 ° C. The drawn yarn was annealed in a set of drums 122 and 124 maintained at a temperature of 165 ° C. The annealing time for the yarn It was 0.2 seconds.

The fully drawn yarn was relaxed at a temperature of 165 ° C between stretch and cold drums 126 with a shrinkage of 12% to obtain the desired stress-strain curve (Figure 2). The initial thread modulus was 57 gram / denier, the strain at 1 gram / denier and 1.5 gram / denier was 4% and 10%, respectively. The resistance to thread breakage was 6.9 gram / denier. The denier of each filament is 13. The initial effort barrier was 0.87 gram / denier. All the above steps, reaction of PET with e-caprolactone, spinning, cooling, stretching and relaxation can be carried out either stepwise in a batch process or more profitably in the form of a continuous process. The previous example describes a continuous process. The previous thread was woven and dyed in a fabric for safety belt. The car collision tests using a sled test showed the performance of the seat belt load limit and the reduction of occupant injury criteria,. In the sled test, the average-sized manikin was restrained with seatbelt fabric and fully instrumented in a compact vehicle. The sled test was conducted at a speed of 40 miles per hour and at an impulse rate of 28 g (which is the acceleration of gravity). The movement of the manikin and injury criteria were recorded by sensors and high-speed cameras. Figure 5 illustrates the performance (with load versus time) of the load-limiting safety belt of the present invention in the torso position in a vehicle collision. Table 1 compares PET seatbelt and load limitation fabrics and shows the reduction of force against the occupant and the improvement of injury criteria. As experts in the field know, the number of references is 74-14; 49 C.F.R., parts 571, 572 and 585, the pulse rate means the acceleration expressed as a manifold of g (which is the acceleration of gravity). HIC means criterion of head injuries. Chest mm (chest mm) refers to the chest deviation of the occupant of the vehicle. Test No. Impulse Lap (KN) Torso (KN) HIC Example of 28 g 436 compliance 40 mph with the present invention Example of 40.5g 8.5 9.7 974 comparison 36 mph No. Test Chest (g) Chest (mm) Pelvis (g) Femur KN Example of 45 36.3 40 0.9 / 1.4L compliance 1 / 2-0.2R with the present invention Example of 59.9 64 55.9 1.8 / -4.5L comparison 1.8 / -1.6R

Claims (1)

CLAIMS A yarn having a force-displacement profile such that: (a) when said yarn is subjected to an initial stress barrier of approximately 0.8 grams / denier to an effort less than or equal to approximately 1.2 grams / denier, said yarn will be it stretches less than 5% and has an initial modulus within a range of about 30 grams / denier to about 80 grams / denier; (b) by subjecting said yarn to an effort greater than said initial stress barrier and at an effort less than or equal to about 1.5 grams / denier, said yarn is further lengthened to at least about 8%; and (c) by subjecting said yarn to an effort greater than 1.5 grams / denier, the modulus is strongly increased and said yarn is further lengthened until said yarn breaks at a tensile strength of at least about 6 grams / denier. , wherein said yarn comprises a multiplicity of fibers, all those fibers substantially have the same force-displacement profile, and are made from polymers having a glass transition temperature within a range from about -40 ° C to about + 70 ° C. The yarn according to claim 1, wherein in part (a), said yarn is stretched to less than about 3%. The yarn according to claim 1, wherein in part (a), said initial module is located within a range of about 40 to about 60 grams / denier. The yarn according to claim 1, wherein in part (b), said yarn is elongated by at least about 10%. The yarn according to claim 1, wherein said yarn is made of a block copolymer of aromatic polyester and lactone monomer and said block copolymer has a glass transition temperature within a range of about + 20 ° C to about + 60 ° C. The yarn according to claim 5, wherein said aromatic polyester is polyethylene terephthalate. The yarn according to claim 6, in where polyethylene terephthalate has an intrinsic viscosity which is measured in a 60/40 by weight mixture of phenol and tetrachloroethane at 25 ° C and is at least about 0.8 deciliters per gram. 8. The yarn according to claim 5, wherein the lactone monomer is e-caprolactone. The yarn according to claim 8, wherein the amount of said e-caprolactone is from about 10 to about 30% by weight of said block copolymer. A process comprising the steps of: (A) transporting an aromatic polyester melt to an injection position in a twin screw extruder wherein said aromatic polyester melt has (i) an intrinsic viscosity that is measured in a mixture 60/40 weight of phenol and tetrachloroethane and is at least about 0.6 deciliters / gramme and (ii) a Newtonian melt viscosity which is calculated at at least about 7,000 poise at a temperature of 280 ° C; (B) injecting a lactone monomer into said molten aromatic polyester of said step (A); (C) dispersing said lactone monomer injected into said aromatic polymer melt in such a way that a uniform mixture is formed in less than about thirty seconds; and (D) reacting said uniform mixture from step (C) at a temperature from about 250 ° C to about 280 ° C to form a block copolymer wherein said steps (A) to (D) occur in less than approximately four minutes of residence time in the twin screw extruder. SUMMARY OF THE INVENTION The present invention provides a yarn having a force-displacement profile such that: (a) when the yarn is subjected to an initial stress barrier of about 0.8 gram / denier to a level less than or equal to about 1.2 grams / denier, the yarn is stretched less than 5% and has an initial modulus in the range of about 30 grams / denier to about 80 grams / denier, (b) by subjecting the yarn to an effort greater than the barrier initial effort and at a level less than or equal to approximately 1.5 grams / denier, the yarn is further lengthened to at least about 8%; and (c) by subjecting the yarn to an effort greater than

1.5 grams / denier, the modulus is increased significantly and the yarn is further lengthened to its breaking at a tensile strength of at least about 6 grams / denier, wherein the yarn comprises several fibers, all fibers have substantially the same force-displacement profile, and polymers having a glass transition temperature within a range of about -40 ° C to about + 70 ° C are made. The present invention also provides a process for making block copolymer and a process for making a charge limiting yarn from the block copolymer. The yarn fabric of the present invention is useful for belts of safety, harnesses and chords for parachutes, shoulder harnesses, cargo handling, safety nets, trampolines, safety belts or harnesses for workers who work in high places, military arrest tapes to slow down aircraft, drag lines skis and in rope applications such as for mooring yachts or for mooring towers on oil wells.