MXPA99007540A - Air bag fabric possessing improved packed volume characteristics - Google Patents

Abstract

A fabric for use in an air bag (12) is provided. The fabric of the invention is produced by mechanically compressing a preliminary fabric constructed substantially of synthetic yarn (24, 26) such that the packed volume per unit area of the compressed fabric is less than the packed volume per unit area of the preliminary fabric. Air permeability is not adversely affected.

Description

FABRIC FOR AIR BAG WITH BETTER VOLUME CHARACTERISTICS IN STATE PACKAGED FIELD OF THE INVENTION The invention relates, in general, to a synthetic filament yarn fabric for use in the manufacture of an air pocket and, more particularly, to mechanically compressed fabric structures that can be packaged in small volumes. without unduly affecting the air permeability.

BACKGROUND OF THE INVENTION In general, it is required that the fabrics used for the manufacture of air bags have limited and controlled air permeability. As will be appreciated, these fabrics are generally woven structures formed of synthetic yarns composed of a plurality of individual filaments. The formation of these fabrics can be done on weaving machines using air injection, water injection or mechanical means for the insertion of fill yarns between a plurality of warp yarn in a manner well known to those skilled in the art. These woven fabrics are described, for example, in U.S. Patent Nos. 5,566,434 to Beasley, 5,508,073 to Krummheuer et al .; 5,503,197 by Bower et al .; 5,356,680 to Krummheuer et al .; 5,421,378 to Bower et al; 5,277,230 to Sollars, Jr .; 5,259,645 to Hirabayashi et al; 5,110,666 to Menzel, et al .; 5,093,163 to Krummheuer et al .; 5,073,418 to Thornton et al .; 5,011,183 to Thornton et al .; 4,977,016 to Thornton et al .; 4,921,735 of Bloch and 3,814,141 of Iribe et al. (all specifically incorporated as reference). As will be appreciated, very low, controlled air permeability can be achieved by using coatings applied in the manufacture of the fabric. The main coatings that have been used are chloroprene (neoprene), silicone and other elastomeric resins. However, the use of such coatings presents a disadvantage from the economic and functional point of view. Specifically, the use of coatings can substantially increase the cost while at the same time increasing the size of the finished product which results in a higher volume bending in the final configuration thus requiring much more space within the vehicle deployment system to your accommodation. In order to avoid the use of coatings while at the same time achieving low and controlled air permeability, a large number of procedures have been taken. The Patents of Thornton et al. and Bloch propose to achieve low permeability through the use of pressing to close the gaps in the interstices between the superposed yarns of the fabric. While these pressing operations can reduce permeability, such operations also harden the fabric and thereby increase the volume requirements for a packed bag formed of such pressed material. The fabrics have also been produced using extremely hermetic knitted constructions and in this way the yarns are packed so tightly together to achieve the desired low air permeability. Such known construction is a 420 denier nylon 6,6 fabric having 57 threads per inch in the warp and 53 threads per inch in the fill and sold under the MICROPERM ™ brand by Milliken & Company in LaGrange, Georgia. A problem associated with this practice is once again the fact that the fabric produced may have relatively little capacity to bend due to the large number of threads per inch inside the woven construction which increases its hardening and therefore the volume requirements for packed. The volume for packaging (ie the ability to bend) becomes an important characteristic of the fabrics for air bags. Specifically, a good ability to bend is crucial if the airbag will be accommodated in the steering wheel of motor vehicles in a very small amount of space. further, a good ability to bend also makes possible an inflation without problems of the airbag to protect the occupant of the vehicle in the event of a crash. In addition, these aspects of packaging and inflation without problems make the folding patterns that are used to control the initial shock even more important in situations where an occupant can be directly confronted with the deployment of the cushion. The difficulty in improving the ability to bend is that the procedures that are recognized, in general, to improve the draping of the fabric and by this means its ability to bend such as, for example, in the physical, pneumatic or hydraulic practices of Shock also tend to increase the permeability of the fabric to the air. In U.S. Patent No. 5,508,073 to Krummheuer et al. (incorporated by reference), it has been proposed that the ability to bend of an airbag fabric can be achieved without sacrificing air permeability if yarns having very low linear density filaments are used in construction. In light of the foregoing, there is a need for a fabric to be used in an air bag, which can be produced with a better ability to bend without sacrificing physical properties and without being limited to the use of low DPF yarns. The present invention provides this cloth and the methods for its production and, therefore, represents a very useful advance in the state of the art.

DESCRIPTION OF THE INVENTION In recognition of the aforementioned and other limitations in the prior art elaborations, it is a general object of the present invention to provide an air bag fabric with a better capacity to be folded which can be made from from a wide range of yarn types. It is another object of the present invention to provide an air bag fabric with improved bent capacity wherein such improved ability to be bent is achieved by means of low cost mechanical treatment processes, without substantially increasing the air permeability characteristics of the cloth. It is still another object of the present invention to provide an airbag fabric with a better capacity to be folded where such an improvement in the ability to be bent or folded is achieved by means of mechanical treatment processes, which also reduce variations in the Physical properties across the width of the fabric such as those introduced during weaving. Surprisingly it has been found that the above objectives of improved folding that is measured by the packing volume under compression loading and reduction in the variation of the physical properties across the width of the fabric can be achieved by mechanically compressing the fabric without adversely affecting it. the characteristics of air permeability. According to the above, in one aspect of the present invention there is provided a woven fabric, made substantially of synthetic yarn which has undergone a mechanical compression process. The compressed fabric has a packaging volume per unit area of fabric less than the packaging volume per unit area of the fabric before mechanical compression. In another aspect of the present invention, there is provided a woven fabric constructed substantially of synthetic yarn which has undergone a process with which the compressed fabric has a packaging volume per unit area of fabric less than the packaging volume per unit. of a fabric area before the process. In addition, the dynamic air permeability of the fabric is reduced to a level below that of a fabric before the process. Other objects, peculiarities and aspects of the present invention will be apparent from the description of the preferred embodiments and the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS A complete description and enabling to enable the present invention, which includes the best mode thereof, addressed to a person skilled in the art, is more specifically stated in the rest of the specifications, including references to the figures accompanying it in which: FIGURE 1 is a sectional view of a common airbag installation mounted on the steering wheel of an automobile; FIGURE 2 is a view illustrating an airbag of FIGURE 1, in an unfolded state; FIGURE 3 is a schematic view of a section of a potentially preferred processing technique for the fabric according to the present invention; and FIGURES 4A and 4B illustrate a folded construction of an air bag fabric useful in testing the packed volume characteristics (or the volume of the packed fabric); FIGURE 5 shows a device for measuring the packed volume of a fabric according to the present invention; The repeated use of the reference characters in the present specification and the drawings is proposed to represent the general or analogous features or elements of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION It should be understood that the description and exemplification of the potentially preferred embodiments in no sense are proposed as limiting the broader aspects of the present invention, which will be defined solely by the compliance and adherence to the permitted and equivalent claims to them. Referring now to FIGURE 1, a schematic sectional view of a common air bag system on the driver's side 10 is shown. As shown, a common system includes an inflatable, folded air bag 12 placed within a confined module 14 housed within the steering wheel of address 16 or, on the dashboard if it is used to hold on the passenger side. The air bag 12 is commonly formed of fabric 18 and is attached to an inflator 20 which in turn is attached to a shock sensing sensor (not shown). When the deceleration of the vehicle exceeds a certain level, the shock detector sends a signal to the inflator 20 and by this means induces a chemical reaction of a gas generating agent to inflate the air bag 12 into the accommodated position of FIGURE 1 to the inflated position illustrated in FIGURE 2 in relation opposite to the passenger of the vehicle 22. While in the illustrated mode the module 14 is placed inside the steering wheel, it should be appreciated that the module can also be placed in any other place opposite to the passenger of the vehicle, including the dashboard, door panel, or in the front seat, as desired. As will be appreciated, the manufacturing material for the air bag 12 commonly includes at least a portion of woven fabric. Said fabric is generally made of synthetic threads and these threads in turn are formed from a large number of twisted filaments together in known configurations. Generally filaments formed of polyester or nylon are preferred, and filaments formed of nylon 6,6 are more preferred. It is contemplated that suitable linear densities for the yarn used in the fabric, according to the present invention, may vary from about 40 denier to about 1200 denier while the denier of the individual filaments therein may vary from 1 denier to about 10 denier. The fabrics according to the present invention are preferably manufactured in a relatively hermetic construction, using a flat fabric or Panama type. However, diagonal tissues can also be used if desired. By way of illustration only, and not limitation, some common constructions for the fabric according to the present invention are set forth below in Table I.

In view of the data in Table I, it should be understood that filament deniers of about 3 are considered representative of low denier constructions by filaments, whereas constructions of about 6 denier are considered representative of regular constructions. denier by filament. The designation of threads per inch is in the state in which the fabric will be finished. That is, the density of the strand can be obtained in spinning or through finishing (ie in washing and drying). In any case, it should be understood that these constructions are in no sense intended to limit the scope of the invention but are offered only to illustrate the types of airbag fabric that can benefit from other processes that improve the ability to bend (is say, to reduce the characteristics of packaged volume) through an additional process, according to the present invention. The tests were carried out on each of the fabric constructions listed in Table I to evaluate the characteristics of packaged volume and air permeability before and after they were subjected to additional processes, in accordance with the practices of the present invention. Specifically, following the formation and some finishing which may have been decided to achieve the constructions as listed in Table I, then the fabric is subjected to compression forces to force the threads of the fabric to come together, thereby tending to increase the density (mass per unit area) of the resulting fabric by about 4-10 percent or more compared to that of the fabric before compression. In a potentially preferred practice illustrated in Figure 3, the fabric 18 constructed of warp yarn 24 and fill yarn 26 passes close to and in intimate contact with a rubber band 28 in a space between a press roll 30 and a heatable cylinder 32. In this space the rubber band is lengthened due to the curvature around the presser roller and the force exerted by the cylinder. As the rubber band 28 leaves the space, it is rolled up, thereby compacting the fabric, which adheres to the rubber band 28 and slides on the surface of the roller 32. The fabric is preferably held between the band and the cylinder by approximately 180 ° of revolution around the cylinder 32 to allow complete winding. A potentially preferred piece of equipment for use in the practice of such mechanical compression of the fabric 18 is considered to be available by Morrison Textile Machinery Corporation with a business address in Fort Lawn, South Carolina. Although the specific operating parameters that are used in the practice of the process, as illustrated in Figure 3, can vary as desired by those skilled in the art to achieve optimal results, in general, it is considered that to reduce the volume characteristics packaging the fabric 18 without unduly increasing the permeability of the fabric or otherwise degrading the fabric, the temperature of the cylinder 32 must be maintained between near room temperature and about 325 ° F. Temperatures lower than 250 ° F or lower may be preferred. As indicated above, it has surprisingly been found that air bag fabrics that are subjected to such compression actually demonstrate a better ability to be folded depending on the area, compared to that demonstrated before being subjected to such treatment despite of the fact that the cloth after the treatment is denser depending on the area. At the same time, the air permeability of the fabric is not adversely affected and, in fact, in many cases it actually decreases. Thus, the fabric produced unexpectedly presents good properties for use in a folded air bag configuration where the packaged volume and the air permeability represent critical parameters. Measurements of the air permeability dynamics for each of the fabrics are set forth below in Table II, as measurements of packed volume for each fabric of a fixed area of the fabric before and after the process. The reference designations for the fabric correspond to those established in Table I.

As indicated, the air permeability measurements set forth in Table II are for dynamic air permeability, which represents the operation of the fabric under the instantaneous application of differential pressure. It is considered that this dynamic test provides a more realistic representation of the performance of the fabric in an air pocket during a crash, where the bag inflates in a few milliseconds. In fact, when carrying out the test procedures, the equipment is set at a specific desired differential pressure. The set pressure builds up inside a cylinder and runs out quickly through the fabric. The measurement in millimeters per second represents the flow of a gas volume (mm2) through a given area of the fabric (mm2) within a short time (sec) with application of a differential pressure drop defined through the cloth. In regard to the data in Table II, the values are provided by volume packed in the fabric before treatment and after treatment with an applied pressure of 0.4 pounds of force per square inch. Although the operating parameters have been listed with a specific pressure, it should be understood that such measurements are only for comparative evaluation purposes between the fabric that has undergone a treatment to improve the capacity to be bent and the fabric that has not undergone this treatment. evaluated under comparable conditions. The comparative evaluation of the packed volume characteristics for the treated and untreated fabric, as set out in Table II, were made using a test technique and apparatus practically as illustrated in Figures 4A, 4B and 5. Specifically, two square cloth panels 34, 36 with a length of 28 inches on each side, as illustrated in Figure 4A were placed in an overlapping relation to each other to simulate the face and the back of a simple air bag configuration, then of which the seams 37 were applied, as shown. The seams were formed of 138 nylon strands of 8-12 stitches per inch. The resulting double layer fabric configuration was folded into a fan configuration together with the fold lines 38 on each side of the double layer fabric configuration to produce a practically rectangular configuration with fan-shaped folds to along each elongated limiting edge, as shown in Figure 4B. Then, the layered fabric configuration was folded into a fan configuration together with the fold lines 40 at each end to produce a final configuration virtually folded into a frame. As an evaluation, the folded structure of the fabric in the manner described was placed in a test chamber 42 with internal dimensions of 5 inches by 5 inches. A platen 44 machined to conform to the internal dimensions of the test chamber 42 was then lowered into the test chamber attached to an Instron tester, as is known to those skilled in the art. The force applied to the platen 44 is monitored by a device 46. As will be appreciated, the volume occupied by the fabric within the test chamber for any applied force can be determined simply by monitoring the displacement of the stage 44 within of the confinement chamber with the force applied. In addition, by starting with fabric samples with equivalent surface areas which are bent in the same way, a true comparative evaluation of the operation before and after the treatment is possible. It has been found that the application of 10 pounds of force applied by the platen 36 through the 25 square inch orifice of the test chamber (i.e. 0.4 pounds of force per square inch) provides better reproducibility in the evaluation. As can be seen through the reference in Table II, the packed volume of the fabric before the treatment was in each case greater than the packed volume of the fabric after the treatment, when they were measured under the same applied pressure. In addition, this beneficial result was obtained without substantially increasing the air permeability of the fabric. In addition to the aforementioned advantages of improving the ability to bend with preservation of the air permeability characteristic, the fabric processed in accordance with the present invention is considered to further provide the benefit of reducing any variation in physical properties, such as air permeability that can exist across the width of the woven fabric. It is generally understood that these variations are due to the different levels of residual stress induced during the weaving process. Such an effort can be different from thread to thread and from machine to machine due to slight differences in the mechanisms of tightening and accommodation of the thread. These residual stresses introduced during the weaving operation can be reduced by balancing the irregular yarn fold that may exist across the width of the fabric. This can be achieved by subjecting the fabric to mechanical compression, in accordance with the preferred practices of the present invention. The advantages of the fabric according to the present invention can be seen as a result in a more compact air bag system which does not sacrifice air permeability thereby providing the designers with additional flexibility in the choices regarding the use of such. systems. The airbag system consists of the airbag itself, the accommodation of the airbag in the vehicle, and the control system to release the function of the airbag. Other embodiments of the invention, of course, will be apparent to those skilled in the art in consideration of the specification and practice of the invention described herein. However, the intention is that the specification and examples contained in it are considered only as examples, the true spirit and scope being defined only by the permitted and equivalent claims of the same.

Claims (10)

1. CLAIMS A fabric for manufacturing an air bag, produced by a method comprising the following steps: (a) providing a preliminary fabric constructed practically of synthetic yarn, wherein the permeability of the fabric has a packaged reference volume per unit area; and (b) mechanical compression of the preliminary fabric to reduce the packaged volume per unit area and compress the fabric to a level lower than said packaged reference volume per unit area of the preliminary fabric under substantially the same measurement conditions.
2. The invention, as set forth in claim 1, wherein said preliminary web is a fabric as obtained from the loom.
3. The invention, as set forth in claim 1, wherein the dynamic air permeability of the compressed fabric is less than the dynamic air permeability of the preliminary fabric.
4. The invention, as set forth in claim 1, wherein the dynamic air permeability of the compressed fabric is not greater than about 1600 mm / sec at an average instantaneous pressure differential of 50 Kpa.
5. 5. The invention, as set forth in claim 1, wherein in step b, the packaged volume per unit is reduced to at least about 8% compared to the reference value of the preliminary fabric.
6. 6. An air bag made of fabric according to claim 1.
7. 7. An air bag system comprising an air bag according to claim 6.
8. 8. A fabric for manufacturing an air bag, produced by the method comprising the following steps: (a) providing a preliminary fabric constructed practically of synthetic yarn, wherein the preliminary fabric has a packaged reference volume per unit area and a dynamic permeability to the reference air; and (b) processing the preliminary fabric to reduce the packaged volume per unit area and dynamic air permeability compared to the preliminary fabric reference values.
9. 9. The invention, as set forth in claim 8, wherein in step b, the packaged volume per unit area is reduced to at least about 8% compared to the reference value of the preliminary fabric.
10. 10. An air bag made of fabric according to claim 9. An air bag system comprising an air bag according to claim 10.