MXPA00010787A - Discontinuously expandable web materials - Google Patents

Abstract

The present invention is a web material which can be used in the production of large quantities of articles which are assembled from, inter alia, continuously fed web materials. In particular, the web material of the present invention can be expanded by a predetermined amount whilst exhibiting a relatively lowresistance to expansion. This material property is assessed in the Discontinuous Expansion Test which determines the Relative Expansion Tension reduction during the discontinuous expansion. A web material according to the present invention has a Relative Expansion Tension Reduction of at least 50%. Another object of the present invention is the process for making such discontinuously expandable web materials comprising the step of incorporating longitudinal expansion means and optionally tearable expansion obstruction means into the web material.

Description

DISCONTINUOUSLY EXPANDABLE TRACK MATERIALS FIELD OF THE INVENTION The present invention relates to weft materials that can be used in the production of large quantities of articles that are assembled from, inter alia, continuously fed weft materials. In particular, the present invention relates to those weft materials that are capable of expanding by a predetermined elongation with relatively low strength.

BACKGROUND Weft materials are well known in the prior art, especially for use in the industrial manufacture of large quantities of discrete articles. The weft materials typically have a two-dimensional configuration with the longitudinal dimension being substantially greater than the transverse dimension. Usually, the longitudinal dimension of a weft material is also substantially greater than the length of the weft material part actually used in the production of a discrete simple article. During the manufacturing process, the weft material is supplied in longitudinally continuous form and then cut into discrete pieces during the manufacturing process. For many applications, it is preferable to use weft materials that are capable of longitudinally expanding without losing their functionality. These weft materials are especially useful when they are attached to elements of varying sizes or placement. The expansion capacity of the weft material allows them to adapt to a new size or position of the element to which they are fixed.

In some cases, it is desirable that the weft material exhibit a specific elongation behavior. In order to restrict the increase or movement of the fixed element to a certain amount, the weft material must expand by a limited amount only, while exhibiting only a low resistance during the expansion. Once it expands, the weft material must exhibit properties similar to a conventional weft material. In U.S. Patent Nos. 5,518,801 issued to Chappell, No. 5,650,214 issued to Anderson, and in No. 5,691, 035 issued to Chappell, weave materials are disclosed which exhibit performance in the form of elastic. Specifically, these weft materials having an elongation and recovery with a defined and sudden element in the elongation of strength resistance are described where this sudden and definite increase in the strength of resistance restricts the further elongation against the relatively small elongation forces . Although progress has been made towards a weft material that is capable by a predetermined amount, this expansion requires an essentially constant expansion stress. However, there remains the problem of providing a weft material that can be expanded by a predetermined amount with relatively low strength. The present invention is a web material capable of discontinuously expanding having a longitudinal dimension and a transverse dimension substantially smaller than the longitudinal dimension and having at least one longitudinal expansion means, which is characterized in that the reduction of the Relative expansion is at least 50%, preferably at least 75%, even more preferably at least 90%, when a weft material is subjected to the discontinuous expansion test. It is a further object of the present invention to provide a discontinuously expanding weft material having an expansion stress at the discontinuous expansion threshold greater than 1 Newton per 0.0254 meter and having an expansion stress at the expansion point discontinuous less than 0.5 Newton per 0.0254 meter, preferably less than 0.25 Newton per 0.0254 meter, even more preferably less than 0.1 Newton per 0.0254 meter as measured in the discontinuous expansion test. It is still a further object of the present invention to provide a weft material capable of discontinuously expanding that exhibits an elongation relative to the tear point of at least 30%, preferably at least 50% as measured in the discontinuous expansion test. It is an object of the present invention to provide a batch material capable of discontinuously expanding comprising a first region and a second region, wherein the first region has a different weight than the second region. It is still a further object of the present invention to provide said weft material having a relative basis weight deviation of less than 10%, preferably less than 5%, when subjected to the base weight deviation test. It is a further object of the present invention to provide a weft material capable of discontinuously expanding according to which it has a shrinkage tension of less than 0.5 Newton per 0.0254 meter when said weft material is subjected to the contraction force in the discontinuous expansion test. It is a further object of the present invention to provide a discontinuously expanding weft material comprising at least one region exhibiting a monotonously increasing tension force with increasing elongation when the region is subjected to the expansion stress test. It is an object of the present invention to provide a web material capable of discontinuous expansion which additionally comprises at least one tear-off means of expansion clogging. Additionally, it is an object of the present invention to provide a process for making a weft material capable of discontinuous expansion. The process comprises the steps of forming a weft, stabilizing a weft and incorporating longitudinal expansion means as well as tear-off means of obstructing the expansion in the weft material.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1: Expansion voltage curve vs. Relative elongation of a weft material according to the present invention. Figure 2: Expansion voltage curve vs. Relative elongation of a nonwoven web comparative material. Figure 3: Expansion voltage curve vs. relative elongation of a comparative material of film weft. Figure 4: Expansion voltage curve vs. Relative elongation of a weft comparative material exhibiting elastic behavior.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to weft materials which are used in the production of large quantities of articles which are assembled from, inter alia, continuously fed weft materials. Preferably, these weft materials are supplied as a roll and include fibrous webs, non-fibrous webs and foams. The term "weft material" as used herein refers to a material in the form of a sheet, or a mixed or laminated material comprising two or more sheet materials. For example, a weft material may be a fibrous web, a non-fibrous web, a foam, or the like. The weft material of the present invention is essentially two-dimensional, that is, the thickness of the weft material is much smaller than its length and its transverse dimension. Additionally, the transverse dimension of the weft material is substantially less than its longitudinal dimension. The longitudinal dimension preferably exceeds the transverse dimension by a factor of 100, most preferably the longitudinal dimension of the weft material of the present invention is essentially infinite. In addition, the web material of present invention has a first external surface and a second external surface opposite the first surface. The weft material of the present invention may also comprise hidden surfaces including a first and a second concealed surface according to which the outer surface is connected thereto. At least part of each concealed surface is in contact with at least a part of one of another concealed surface such as after bending a conventional weft material. These hidden surfaces may become part of the respective external surface during the expansion of the weft material of the present invention. One embodiment of the weft material of the present invention is a fibrous web, such as a tissue web, a non-woven web, a woven web, an interwoven web, or the like. These fibrous webs can be made from natural fibers (for example wood or cotton fibers), from synthetic fibers (for example, polyester or polypropylene fibers), or a combination of natural and synthetic fibers. The non-woven web materials can be, without being limited thereto, made by commonly referred processes such as spinning, spinning, melt blowing, carding and / or bonding with continuous air or calendering. The fibrous webs of the present invention can be absorbent or non-absorbent, liquid permeable, or liquid impervious. Another embodiment of the weft material of the present invention is the non-fibrous web such as a film. The non-fibrous web materials of the present invention may comprise polyolefins such as polyethylenes, including linear low density polyethylene (LLDPE), low density polyethylene (LDPE), ultra low density polyethylene (ULDPE), high density polyethylene (HDPE) ), or polypropylene and mixtures thereof with the above or other materials. Examples of other suitable polymeric materials that may also be used include, but are not limited to, polyesters, polyurethanes, compostable or biodegradable polymers, heat-shrinkable polymers, thermoplastic elastomers., polymers based on metallocene catalyst (eg, INSITE ™ available from Dow Chemical Company and Exxact ™ available from Exxon), and respirable polymers. The non-fibrous web material may also be composed of an apertured film, macroscopically expanded three-dimensional formed film, absorbent or foam, filled composition, or laminates and / or combinations thereof. The weft materials of the present invention may include laminates of the aforementioned materials. The laminates can be combined by any number of joining methods known to those skilled in the art. These joining methods include but are not limited to thermal bonding, adhesive bonding (using any of a number of adhesives including but not limited to sprayed adhesives, thermal melt adhesives, latex-based adhesives and the like), sonic bonding and extrusion lamination by means of which a polymeric film is emptied directly onto a substrate, and while still in a partially molten state, attached to a substrate side, or by depositing non-woven meltblown fibers directly onto a substrate. Alternatively, the weft material of the present invention can also comprise discretely distributed substances that are fixed to the weft material. An essential element of the weft material of the present invention is that it comprises at least one longitudinal expansion means. The term "longitudinal expansion means" as used herein refers to a means that allows the weft material to expand in the longitudinal direction by a predetermined amount. After this expansion, the weft material preferably exhibits a behavior under longitudinal tension similar to a conventional weft material. Preferably, the longitudinal expansion of a weft material of the present invention is irreversible, after the predetermined longitudinal expansion there is no contraction force pulling back the weft material to its unexpanded configuration. Generally, a region of the weft material whose perimeter coincides with the perimeter of the longitudinal expansion means may be characterized as having a longitudinal surface contour at least partially. As a result, the length of the longitudinal surface contour of this region of the weft material is substantially longer than the longitudinal distance of the two transverse edges that delimit the region. Specifically, the difference between the length of the surface contour and the longitudinal distance between the delimiting transverse edges is the predetermined length of accessible expansion for the region of the weft material comprising the longitudinal expansion means. The term "longitudinal surface contour length" as used herein refers to the length of a region of a weft material by which the length is measured along a possibly curved path that follows the longitudinal dimension of the surfaces external and hidden like these are connected to each other. A preferred embodiment of the longitudinal expansion means of the present invention is a double transverse bend, which upon unfolding allows the weft material to substantially increase its longitudinal dimension. A particularly preferred embodiment of the longitudinal expansion means of the present invention having a curved longitudinal surface contour is comprised in a weft material according to the present invention which is obtained by arranging a conventional precursor weft material in a transverse fold in z. The term "z-transverse bending" as used herein refers to two transverse bends that are arranged such that the longitudinal cross section of the weft material resembles the letter "z" when viewed from the side. Specifically, the first surface of the precursor web material between the first transverse bending and the second transverse bending are in close proximity to the first surface on the opposite side of the first transverse bending and the second surface of the precursor web material between the first transverse bending and the second transverse bending is in close proximity to the second surface on the opposite side of the second transverse bending. The z-fold allows the weft to comprise a longitudinal expansion medium without losing its primarily two-dimensional configuration.

Another preferred embodiment of the longitudinal expansion means of the present invention is a plurality of transverse folds which are in close proximity to each other, called in the following accordion fold. The longitudinal expansion means of the present invention may also be but are not limited to regions of the weft material that are mechanically stressed, plicated, corrugated, "ring-rolled", or folded. The "ring rolling" process is described in U.S. Patent No. 4,517,714 issued to Sneed. All of these treatments have to be carried out in the transverse direction to make the weft material longitudinally expandable. A particularly preferred embodiment of the weft material of the present invention comprises a plurality of longitudinal expansion means which are spaced apart longitudinally allowing the weft material to expand locally at the positions of the longitudinal expansion means. An even more preferred embodiment comprises longitudinal expansion means at longitudinally equal distances to allow a periodic local expansion of the frame when it is converted. Preferably, the weft material of the present invention additionally comprises at least one tear-off means of clogging the expansion. The term "tear-off means of expansion obstruction" as used herein refers to a means which is preventing the longitudinal expansion of a weft material comprising a longitudinal expansion means. In addition, the tear-off means of clogging the expansion is tear-off by means of the longitudinal tension applied to the weft. After tearing of the tear-away means of obstructing the longitudinal expansion, the longitudinal expansion means may be used to longitudinally expand the weft material at the position of the respective longitudinal expansion means.

Generally, the tear-open means of obstructing the expansion of the present invention retain the delimiting transverse edges of a region of the weft material comprising a longitudinal expansion means at a distance less than the length of the longitudinal surface contour between the delimiting transverse edges. . Preferably, the tear-off means of obstructing the expansion prevents relative movement of the hidden surface regions of the weft material that are separated apart along the longitudinal surface contour. This can be achieved by at least the partial direct connection or at least the indirect partial connection such as the edge joint. Tear-open means of clogging the expansion of the present invention include but are not limited to adhesive bonding, ultrasonic bonding, heat bonding, pressure bonding, friction bonding, autogenous bonding or combinations of the different bonding methods. The tear-off means of clogging the expansion can also be a mechanical fastening by a mechanical fastening device such as a bracket, or filament or by fiber entanglement. Alternatively, the tear-off means of expansion obstruction may be the region of the weft material with low or no longitudinal expansion capacity that is longitudinally disposed parallel to the longitudinally expandable region of the weft material. In another preferred embodiment of the weft material of the present invention, the tear-off means of clogging the expansion are placed near the longitudinal edges of the weft material to avoid possible compromise of the integrity of the weft in the center of the weft by tearing the tear-off means of expansion obstruction. Alternatively, the tear-off means of obstructing the expansion can be arranged in separate, separate positions to carry the minimum of compromise. The tear-off means of clogging the expansion can be separated by applying a longitudinal tension to the weft material without tearing the entire weft. In this case the tearing force of the tear-off means of clogging the expansion must be substantially less than the tearing force of the weft material. The screen material of the present invention shows a discontinuous expansion behavior. This expands with relatively low resistance to a certain limit and then shows a rapid increase in the expansion voltage, essentially limiting its expansion to that certain limit. In its unexpanded state, the weft material of the present invention exhibits a relatively higher expansion stress than the expansion stress during limited expansion with the low strength. This allows the conversion of the weft material in its unexpanded state which is followed by a rapid expansion of the weft caused by the longitudinal tension of the increased weft. An expansion voltage vs. Typical relative elongation of the weft material of the present invention is shown in Figure 1. The expansion vs. Relative elongation of the weft material of the present invention exhibits at least two local maxims. The maximum that has the largest elongation corresponds to the point of tearing of the frame while the maximum against the smallest elongation reflects the threshold of the discontinuous expansion. The absolute minimum intermediate between these two maxims is located within the region of discontinuous expansion and will be called point of discontinuous expansion thereafter. Preferably, the weft material of the present invention has a reduction in the relative expansion stress of at least 50%, more preferably 75%, even more preferably 90%. This parameter which is obtained through the discontinuous expansion test disclosed in the present application quantifies how much of the expansion stress of a weft material is reduced when it expands to the point of discontinuous expansion. Figure 2 shows the curve of expansion tension vs. relative elongation for a conventional weft material, exemplified by a non-woven weft material available from Fiberweb Sweden AB of Norrkoping, Sweden, under the designation Holmestra D018B, having a basis weight of 18 grams per square meter. This curve clearly differs from the curve of a weft material of the present invention in that that curve comprises only a maximum expansion tension. Therefore, conventional weft materials such as this non-woven material do not fall within the scope of the present invention. Figure 3 shows the curve of expansion tension vs. Relative lengthening of Example 3, a conventional film weft material available from American National Can of Chicago, Illinois / USA, under the designation Parafilm. This curve also has two local maxima and falls of the expansion voltage by approximately 37% between the two maxima. However, this weft material is not within the scope of this invention since a weft material according to this invention needs to have a reduction of the relative expansion stress of at least 50%. Figure 4 shows the expansion tension of example 4, a weft material having an elastic behavior according to the patent of the United States No. 5,691, 035. This curve only comprises a maximum at the point of tearing. This weft material therefore does not fall within the scope of the present invention.

Preferably, the expansion tension of the weft material of the present invention at the threshold of discontinuous expansion is greater than 1 Newton per 0.0254 meter although the expansion stress at the point of discontinuous expansion is less than 0.5 Newton per 0.254 meter, most preferably less than 0.25 Newton per 0.0254 meter, even more preferably less than 0.1 Newton per 0.0254 meter. A preferred embodiment of the present invention is a weft material comprising a first region and a second region, both regions extending longitudinally and including the total transverse dimension of the weft material, where the second region has a higher basis weight than the first region. . In an even more preferred embodiment of the weft material of the present invention, the second region comprises at least one longitudinal expansion means while the first region does not comprise a longitudinal expansion means. Still more preferably, the basis weight of the second region is chosen such that after expansion by means of the longitudinal expansion elements the basis weight of the second region is essentially similar to the basis weight of the first region. This property is measured using the base weight deviation test. Preferably, the deviation of the relative basis weight of the weft material of the present invention is less than 10%, more preferably less than 5%. The advantage of this particular embodiment is that after the expansion by the predetermined amount the weft material has an essentially uniform basis weight. Preferably, the weft material of the present invention exhibits an overall relative elongation of at least 50% at the Tear Point when subjected to the Discontinuous Expansion Test, more preferably an overall relative elongation of at least 75%.

Preferably, the base material of the present invention or at least one region thereof which is comprising at least one longitudinal expansion means that is capable of expanding at least 50%, more preferably at least 100%, including more preferably at least 150% of its original dimension not stressed after deactivation of the tear-off means of expansion obstruction. The relative expansion capacity is quantified with the Expansion Test after Deactivation disclosed in this application. Another aspect of the present invention is the process for making a weft material according to the present invention. Alternatively, the weft material of the present invention can also be obtained by modifying a conventional weft material. Preferably, the process of the present invention for making a weft material comprises the steps of (A) forming a weft material, (B) stabilizing the weft material, (C) incorporating the unexpanded longitudinal expansion means into the material. weft, (D) incorporating the deactivation means of expansion obstruction in the weft precursor material, and optionally, (E) unrolling the weft material, optionally, (F) longitudinally cutting the weft material, optionally, ( G) rewind the weft material. In this, the combination of incorporating the means the combination of incorporating the means of longitudinal expansion into a conventional precursor web with the incorporation of the deactivating means of obstruction of the expansion in order to avoid the expansion of the longitudinal expansion means allows the production of weft materials according to the present invention. The order of the steps does not necessarily have to be in the previous order. It is possible to carry out step B at any point after step A, particularly after step D. Steps C and D can also be carried out intermediate to steps E and G or after step G. Preferably, the step of incorporating the longitudinal expansion means into the weft material is carried out by bending the weft transversely, still more preferably in a fold at zo in an accordion fold. Alternatively, the longitudinal expansion means are incorporated into the weft by pre-stretching at least partially the weft material to make it longitudinally expandable. The possible processes for this task are cornered, corrugated, "ring rolled", or folded. All of these treatments have to be carried out in the transverse direction to make the weft material longitudinally expandable. Preferably, the deactilable means of obstructing the expansion are incorporated into the weft material by joining the surfaces or edges that are spaced apart along the surface contour. These surfaces or edges have been brought in close proximity to each other by incorporating the longitudinal expansion means into the weft material. Possible methods to achieve these bonds include, but are not limited to, adhesive bonding, ultrasonic bonding, thermal bonding, pressure bonding, friction bonding, autogenous bonding or combinations of different bonding methods. Alternatively, the joints can be achieved by incorporating mechanical fastening devices such as brackets, wires, or the like, into the weft material. Another possibility for incorporating the deactivable means of obstructing the expansion in the weft material is the entanglement of the fibers of different surface regions or edge, for example, by stitching, hydroentanglement, or the like.

EXAMPLES Example 1: Z-folded nonwoven web material This example is provided to demonstrate the principle of the present invention. A glued-blown spunbond nonwoven web material glued, available from Corovin GmbH of Peine, Germany, under the designation MD3000, consisting mainly of polypropylene fibers was cut into a longitudinal strip having a length of 20 mm. centimeters and a width of 2.54 centimeters. The weft material was arranged in a transverse fold in z by the following steps: In localized positions of 5 and 8 centimeters away from one of the transverse edges, the strip of the weft material was folded transversely. The transverse fold located at 8 centimeters was folded back over the weft material reaching approximately 2 centimeters away from the transverse edge. To ensure bending in z, the longitudinal edges of the three layers forming the z-fold were heat-bonded to a depth of 1 millimeter, applying a temperature slightly higher than the melting point of the fibers of the non-woven weft material. . The final length of the strip with the z-fold of the weft material was 140 millimeters. The reduction of the elastic modulus of Example 1 was 99% when it was subjected to the expansion blocked deactivation test.

Example 2: Comparative Nonwoven Weft Material Example 2 is a spunbonded nonwoven web material made of polypropylene fibers having a basis weight of 18 grams per square meter. The plot material is available from Fiberweb Sweden AB of Norrkoping, Sweden, under the designation Holmestra D018B.

Example 3: Film Weave Comparison Material Example 3 is a polymer film weft material available from American National Can of Chicago, Illinois / USA, under the designation Parafilm.

Example 4: Weft comparative material having an elastic behavior Example 4 is a thin polymeric film weft material generally consisting of medium density linear polyethylene plus linear low density polyethylene available from Tredegar Inc. of Terre Haute, Indiana / USA, under the designation X-8998 which has been formed in accordance with the patent of the States United No. 5,691, 035.

METHODS Expansion voltage test The expansion stress test is used to measure the expansion tension properties against the percent elongation. These tests are performed on a standard stress-strain curve measurement device such as a Zwick model 1445, available from Zwick GmbH & Co. of Ulm, Germany, which is connected to a Compaq Prolinea 466 computer available from Compaq Computer Corporation of Houston, Texas / USA, which utilizes Zwick 7047.4b software which is available from Zwick GmbH & Co. of Ulm, Germany. All the essential parameters needed for the test are entered into the Zwick 7047.4b program for each test. Also, the entire data collection, data analysis and graphing are done using the Zwick 7047.4b program. The samples used for this test are 25.4 millimeters wide by 140 millimeters long with the long axis of the sample cut parallel to the longitudinal dimension of the weft material. The sample should be cut with a sharp die cutter or some suitable pointed cutting device designed to cut a sample of (25.4 +/- 1) millimeters wide. The sample must be cut in such a way that an area representative of the longitudinal expansion medium is represented. There will be cases (due to variations in any of the size or distance of the longitudinal expansion medium) in which it will be necessary to cut off any of the larger or smaller samples than what is suggested there. In this case, it is very important to notice (along with any reported data) the sample size, whose area of the weft material was taken, and preferably includes a schematic diagram of the representative area used for the sample. Also, the results need to be calculated taking into account the different length. Three samples of a given material are tested. The clamps of the apparatus consist of air operated jaws designed to concentrate the total grip force along a single line perpendicular to the direction of the test stress having a flat surface of an opposite face from which a round half protrudes to minimize the slippage of the sample. The distance between the lines of the gripping force must be 100 millimeters as measured by a steel rule held under the jaws. This distance will be referred to from this as the "length of measurements". The sample is mounted on the jaws with its long axis perpendicular to the direction of the percent elongation applied. The crosshead speed is set at 500 millimeters per minute. The crosshead lengthens the sample until the sample breaks. The result is a curve of the expansion voltage as a function of the relative elongation of the weft material that is obtained. Although the test methods described above are useful for many of the weft materials of the present invention, it is recognized that the test method can be modified to encompass some of the more complex weave materials within the scope of the present invention.

Proof of discontinuous expansion The discontinuous expansion test is used to determine the discontinuous expansion threshold, the tear point and the reduction of the relative expansion stress of a weft material. First, three identical samples of the raster material, called samples A1, A2, and A3, are submitted to the expansion voltage test. From the resulting curve of the expansion voltage vs. the relative elongation for the sample A1, the local maximum of the expansion is obtained together with the respective relative elongations (the weft material subjected is not capable of discontinuously expanding according to the present invention if the expansion voltage curve vs. relative elongation comprises only a maximum). The local maximum having the smallest elongation is called the discontinuous expansion threshold with a respective expansion voltage of T1 and a respective relative elongation E1. The local maximum having the largest elongation is called the tear point with a respective expansion voltage T2 and a respective relative expansion E2. Now, the absolute minimum of the intermediate expansion voltage to E1 and E2 is obtained from the curve of expansion voltage vs. relative elongation of the weft material. The minimum is called discontinuous expansion point having a respective expansion voltage T3, and a respective relative elongation E3. The same procedure is carried out for samples A2 and A3. Finally, the expansion tensions T2 and T3 are averaged for the three samples and the reduction of the relative expansion voltage RETR of the weft materials supplied through the formula RETR = (T2A-T3A) / T2A where T2A is obtained and T3A are the respective averages of T2 and T3. • Proof of the deviation of the base weight This test is used to determine the uniformity of the basis weight of a weft material after it has been expanded by a certain amount and then it is allowed to detect a certain type of weft expandable materials. Six identical samples of the supplied raster material, called samples A1, A2, A3, B1, B2 and B3 are prepared in the following, according to the sample preparation described in the expansion voltage test. Each sample must comprise at least one longitudinal expansion means. In the event that the sample size of the expansion stress test is insufficient to meet this requirement, the expansion stress test has to be modified to encompass sufficiently large samples of the weft material. Sample A1 is subjected to the expansion voltage test. From the resulting curve of the expansion voltage vs. relative elongation, that point of the curve having the same expansion voltage as the discontinuous expansion threshold and the smaller relative elongation greater than the relative elongation corresponding to the discontinuous expansion threshold is determined. This point will be called the point of total expansion. (If the total expansion point does not exist, then the submitted raster material is not able to expand discontinuously and is not capable of being tested according to this test.) This procedure is repeated with samples A2 and A3. The relative elongation E4 is computed by averaging over the relative elongation of the total expansion points of samples A1, A2, and A3. Sample B1 is mounted on the jaws of a Zwick model 1445, available from Zwick GmbH & amp;; Co. of Ulm, Germany, in accordance with the instructions of the expansion voltage test. Subsequently, the sample B is expanded to the relative elongation E4 using the Zwick 1445. Finally, five square pieces of a weft material having an area of (1 +/- 0.01) square centimeters from the sample B1 are cut. The positions in which the pieces are cut out should be chosen equally distributed along the longitudinal dimension of the sample B1 and should be centered with respect to the transverse direction. All these pieces of the weft material are weighed with a precision of one microgram. The same procedure is carried out with samples B2 and B3. The deviation of the relative basis weight is obtained by dividing the standard deviation of the weights of the 15 pieces of the weft material between the average weight of the pieces.

Test of the contraction tension in discontinuous expansion This test is used to determine the contraction stress at the point of discontinuous expansion.

Six identical samples of the subject web material are prepared, called samples A1, A2, A3, B1, B2, and B3 subsequently, according to the preparation of the sample described in the expansion stress test. Sample A1 is subjected to the expansion voltage test. From the resulting curve of the expansion voltage vs. relative elongation, the point of the discontinuous expansion is determined. The same procedure is carried out for samples A2 and A3. The resulting relative elongations E3 are averaged, the average is called E3A later. Sample B1 is mounted on the jaws of a Zwick model 1445, available from Zwick GmbH & Co. of Ulm, Germany, in accordance with the instructions of the expansion stress test. Subsequently, the sample B2 is expanded to the relative elongation E3A which corresponds to the point of the discontinuous expansion using the Zwick 1445. After the jaws of the Zwick model 1445 have been stopped, the force trying to reduce the longitudinal extension of the plot. The same procedure is carried out for samples B2 and B3. Finally, the contraction tension is obtained by averaging the measured forces for samples B1, B2 and B3. Although the methods described above are useful for many of the weft materials of the present invention, it is recognized that the test method would have to be modified to encompass certain executions of the weft materials within the scope of the present invention.

Claims (15)

1. A weft material having a longitudinal dimension and a transverse dimension substantially less than the longitudinal dimension, at least one longitudinal expansion means characterized in that the reduction of the relative expansion stress is at least 50% when the material is subjected to plot to discontinuous expansion test.

2. A weft material according to claim 1, characterized in that the reduction of the relative expansion stress is at least 75% when the weft material is subjected to the discontinuous expansion test.

3. A weft material according to claim 1, characterized in that the reduction of the relative expansion stress is at least 90% when the weft material is subjected to the discontinuous expansion test. A weft material according to claim 1, characterized in that the expansion stress at the discontinuous expansion threshold is greater than 1 Newton per 0.0254 meters and the expansion stress at the discontinuous expansion point is less than 0.5 Newton per 0.0254 meters when the weft material is subjected to the discontinuous expansion test. A weft material according to claim 1, characterized in that the expansion stress at the discontinuous expansion threshold is greater than 1 Newton per 0.0254 meters and the expansion stress at the discontinuous expansion point is less than 0.5 Newton per 0.0254 meters when the weft material is subjected to the discontinuous expansion test. A weft material according to claim 1, characterized in that the expansion stress at the discontinuous expansion threshold is greater than 1 Newton per 0.0254 meters and the expansion stress at the discontinuous expansion point is less than 0.1 Newton per 0.0254 meters when the weft material is subjected to the discontinuous expansion test. A weft material according to claim 1, characterized in that the relative elongation at the point of tearing of the weft material is at least 50% when the weft material is subjected to the discontinuous expansion test. A weft material according to claim 7, characterized in that the relative elongation at the point of tearing of the weft material is at least 75% when the weft material is subjected to the discontinuous expansion test. 9. A weft material according to claim 1, comprising a first region and a second region characterized in that the first region has a different basis weight than the second region. A weft material according to claim 9, characterized in that the weft material has a deviation from the relative basis weight of less than 10% when subjected to the base weight deviation test. A weft material according to claim 9, characterized in that the weft material has a deviation from the relative basis weight of less than 5% when subjected to the base weight deviation test. A weft material according to claim 1, characterized in that the weft material has a shrinkage stress of less than 0.5 Newton per 0.0254 meters when the weft material is subjected to the shrinkage force test in discontinuous expansion. 13. A weft material according to claim 1, comprising at least one characterized region in which the region exhibits a monotonically increasing tensile force with increasing elongation when the region is subjected to the expansion stress test. A weft material according to claim 1, comprising at least one longitudinal expansion means characterized in that the weft material further comprises at least one tear-off means of expansion obstruction. A process for preparing a weft material comprising the steps of: - forming a weft - stabilizing said weft - incorporating longitudinal expansion means and tear-off means of obstructing the expansion in said weft.