EP2292818B1 - Method for producing an elastic string and elastic string obtained - Google Patents

Abstract

The method involves applying overtwist to base wires (20, 30) in direction (S, Z), respectively, and fixing the overtwist of the base wires for stabilizing the wires. The twisted base wires are assembled for forming an elastic string (10) such that the twisted base wires are spaced in a longitudinal axis (A) of the string and oriented in a direction of an axis perpendicular to the longitudinal axis when the string is in free state without traction.

Description

Technical area:

The present invention relates to a method for manufacturing an elastic string or the like, from an assembly of at least two basic threads made of fibers and / or filaments.

Prior art:

In the present invention, the term "string" is not limiting and refers to any linear textile product, of any size or title (from a millimeter to a few centimeters), obtained from an assembly of at least two basic yarns made of fibers and / or filaments, in any natural material (animal and / or vegetable and / or mineral) and / or chemical (synthetic and / or artificial), called according to the applications: thread, string, cord, rope, etc. ., and used in any type of application such as industry, furniture, boating, agri-food, medical, etc.

Elasticity is defined in the following way: it is the quality of an object to be deformable while resuming its original form when the constraint applied to it disappears. In the field of textiles, the final elasticity of the product depends on the elasticity of the yarn used and its manufacturing process. Some synthetic or artificial fibers have their own elasticity. But for natural fibers, the elasticity is limited or even zero. The present invention provides a solution for providing elasticity to the final product made from any type of fibers and / or filaments, including from natural fibers.

There are already elastic strings on the market.

For example, publications are known BE 621 724 A and DE 29 28 692 A an elastic string obtained by twisting together at least two base yarns previously over-twisted in one direction "S" for one and in the other direction "Z" for the other, and then subjecting them to a heat treatment for to stabilize their torsion.

Some elastic strings are also manufactured by wrapping, an example of which is illustrated in the publication EP 1 746 189 A1 . Grape wrapping is a method of assembling a core wire with a wire wrapped around the core wire which is called a wire wrapper. In most cases, the core wire is a spandex, latex or similar yarn, of fairly large size (about 2 mm in diameter), and is coated with one or more cotton or polyester threads. . This manufacturing process is controlled and the production yield is high. Thus, the product obtained is cheap. Nevertheless, wrapping has major disadvantages. The core wire is not integral with the coating wire. In fact, when the elastic gimped string is cut, it is common that the ends fray or loosen, leaving apparent the core thread. This phenomenon poses serious technical problems in the case where this string is worked on industrial machines. Indeed, the recovery of the cut end is more difficult and can cause malfunctions or even stops the production line. The elastane or latex core yarn has a high elongation rate of up to 700%. This nervousness is such that it can, for certain uses, pose technical problems. Elastane and latex, on the other hand, can not be used in certain environments or for certain applications. In addition, the latex has allergenic properties. Finally, when this string is used in areas where the presentation of the tied product is important, the ends that fray degrade the product. Likewise, its size and rubbery appearance are detrimental to the brand image of the product.

A particular case concerns the use of a gimped elastic string in the food industry, particularly for tying meat pieces, such as paupiettes, roasts, poultry, etc., to ensure the maintenance of different pieces of meat, decoration, stuffing, etc. during cooking. Depending on the quality of the products, the meat can shrink and the string used must be able to follow the retraction of the piece of meat while keeping it tight. In addition to the disadvantages of the covering described above, there is a physical problem: after cooking and during cutting, the elastic gimped string retracts rapidly and causes splashes of cooking juices, sauce and the like, in its environment. This disadvantage does not exist with a traditional non-elastic string. But in this case, the traditional non-elastic string does not ensure effective maintenance of the piece of meat throughout its cooking and is difficult to mechanize. It must be placed manually to avoid cutting the meat in case of automatic break.

To date, there is no satisfactory solution.

Presentation of the invention

The present invention aims to provide a solution to the problems mentioned above by proposing a method of manufacturing an elastic string without elastane or latex, having a high power of retraction and whose elasticity is controllable and can be stabilized or even neutralized under certain conditions to avoid the disadvantages mentioned above.

For this purpose, the invention relates to a method of manufacture of the kind indicated in the preamble, in which one applies an over-twist in a direction S to a first basic thread and an over-twist in the other direction Z to a second base yarn, such that the fibers and / or filaments form an angle β between 30 ° and 90 ° with the longitudinal axis of said first base yarn and said second base yarn is fixed the over-twist of said yarns In order to stabilize them, said overwired basic threads are assembled by a braiding process to form said twine so that, when said twine is in the free state without traction, said over-twisted basic threads have a tendency to away from the longitudinal axis of the string and to orient itself in the direction of an axis perpendicular to said longitudinal axis of the string by forming an angle α with the longitudinal axis of the string between 30 ° and 90 °.

Thus, this manufacturing process makes it possible to impart great elasticity to the twine made by combining an over-twist of the base yarns with a particular assembly of these basic yarns, without the addition of elastane or latex, the elongation at the rupture obtained which may be at least between 20% and 150%.

It is preferred to use base wires whose title is relatively thin and at least between Nm150 and Nm17 (or between 6 tex and 60 tex).

In the formula defining the twist: T = k√Nm, where T is the value of the twist in r / m and Nm is the metric number of the yarn, a high torsion coefficient k is advantageously chosen between at least 200 and 600 .

More than two basic threads can be used to make said string. In this case, one applies to a portion of the base son a superstructure S and the other part of the base son a Z-over-torsion, these parts may be equal.

The over-twist on said base yarns may be fixed by a vaporizing process or any other equivalent method.

In a preferred embodiment of the invention, at least four basic yarns and a braiding machine are used, and the over-twisted basic yarns are arranged in a first direction S on the spindles of the braiding machine going into counterclockwise and the over-twisted basic yarns in the other direction Z on the spindles of the braiding machine going clockwise.

It is possible to use a braiding machine having a number of spindles greater than the number of basic threads to be assembled. In this case, the basic son is arranged on at least one spindle out of two.

The invention also relates to an elastic string obtained by the manufacturing method as described above, characterized in that it comprises a braided assembly of at least four basic threads made of fibers and / or filaments, two first base yarns with one S-direction over-torsion and two second base yarns with Z-direction over-twisting, the fibers and / or filaments of the base yarns forming an angle B included in less between 30 ° and 90 ° with the longitudinal axis of each base wire; and the base yarns deviating from the longitudinal axis of the braided string and orienting towards an axis perpendicular to that longitudinal axis of the string at an angle α with the longitudinal axis of the twine included between 30 ° and 90 °.

Brief description of the drawings:

• la figure 1 est une vue schématique et agrandie d'une tresse obtenue à partir de fils de base en Z et en S selon l'art antérieur,
• la figure 2 est une vue similaire à la figure 1 d'une tresse obtenue à partir de fils de base en S et en Z selon l'invention,
• la figure 3 est un diagramme illustrant la résistance à la traction du fil en fonction de sa torsion,
• la figure 4 est une photographie par microscope d'une tresse de l'art antérieur, et
• la figure 5 est une vue similaire à la figure 4 d'une tresse selon l'invention.

The present invention and its advantages will appear better in the following description of an embodiment given by way of non-limiting example, with reference to the appended drawings, in which:

• the figure 1 is a schematic and enlarged view of a braid obtained from basic son Z and S according to the prior art,
• the figure 2 is a view similar to the figure 1 a braid obtained from base son S and Z according to the invention,
• the figure 3 is a diagram illustrating the tensile strength of the yarn as a function of its twist,
• the figure 4 is a microscope photograph of a braid of the prior art, and
• the figure 5 is a view similar to the figure 4 a braid according to the invention.

Illustrations of the invention and embodiment example:

The process according to the invention (cf. Fig. 2 ) makes it possible to manufacture a string 10 or any similar product such as thread, cord, rope, etc., from an assembly of at least two base yarns 20 and 30, themselves made of fibers and / or filaments 40, the twine 10 obtained having high elastic properties, moreover controllable, without using elastane, latex or the like. The number of basic threads is not limited to two and it is of course possible to manufacture a string according to the invention from an assembly of several basic threads.

• Etape 1) Appliquer une sur-torsion dans un sens S à un premier fil de base 20 et une sur-torsion dans l'autre sens Z à un deuxième fil de base 30. Cette sur-torsion confère une élasticité aux fils de base 20 et 30 car les fibres et/ou filaments 40 forment un angle β avec l'axe longitudinal du fil de base 20, 30 (cf. fig. 2) plus grand que dans le cas d'un fil 2, 3 ayant une valeur de torsion classique (cf. fig. 1), cet angle β étant au moins compris entre 30° et 90°,
• Etape 2) Fixer la sur-torsion des fils de base 20, 30 pour les stabiliser,
• Etape 3) Assembler les fils de base 20, 30 pour former la ficelle 10 de sorte que lorsque la ficelle est à l'état libre sans traction, les fils de base 20, 30 sur-tordus ont tendance à s'écarter de l'axe longitudinal de la ficelle 10 et à s'orienter en direction d'un axe perpendiculaire à cet axe longitudinal en formant un angle α avec l'axe longitudinal A de la ficelle (cf. fig. 2 et 5) plus grand que dans le cas d'une ficelle 1 classique (cf. fig. 1 et 4), cet angle α étant compris entre 30° et 90°.

This manufacturing process comprises at least the following steps:

• Step 1) Apply an over-twist in a direction S to a first base wire 20 and an over-twist in the other direction Z to a second base wire 30. This over-torsion imparts elasticity to the base wires 20 and because the fibers and / or filaments 40 form an angle β with the longitudinal axis of the base wire 20, 30 (cf. Fig. 2 ) larger than in the case of a wire 2, 3 having a conventional torsion value (cf. Fig. 1 ), this angle β being at least between 30 ° and 90 °,
• Step 2) Fix the over-twisting of the base wires 20, 30 to stabilize them,
• Step 3) Assemble the strands 20, 30 to form the string 10 so that when the string is in the free state without traction, the over-twisted base strands 20, 30 tend to deviate from the string. longitudinal axis of the string 10 and to be oriented in the direction of an axis perpendicular to this longitudinal axis by forming an angle α with the longitudinal axis A of the string (cf. Fig. 2 and 5 ) larger than in the case of a classical string 1 (cf. Fig. 1 and 4 ), this angle α being between 30 ° and 90 °.

In the case where more than one base yarn is used, an even number of base yarns are preferred and split into two equal parts to balance the number of over-twisted S-baseline yarns and the number of basic yarns. The over-twist value applied to each of the basic threads may be the same or different depending on the desired results. Of course, any combination of basic threads in quality, number, value of torsion, etc. is possible.

où k correspond au coefficient de torsion et Nm correspond au titre du fil.The twist of the wire can be carried out in the S direction or in the Z direction (cf. Fig. 1 and 2 ). The value of the torsion expressed in revolutions / meter is calculated with the Koechlin formula: $$T\left(\mathit{towers}/m\right)k\sqrt{\mathit{nm}}$$

where k corresponds to the torsion coefficient and Nm corresponds to the title of the wire.

The figure 3 illustrates the curve of the tensile strength (R) of the yarn as a function of its torsion value (T). There is a saturating twist (Ts) where the tensile strength is the highest. Beyond this, the tensile strength of the wire drops to the critical twist (Tc) where the wire breaks.

Depending on the destination of the yarn, it can be twined with other yarns to ultimately produce a larger, more tensile yarn. This is called twisting and the resulting yarn is called twisted yarn or double-stranded or stranded or multi-stranded wire or ends.

The main effect of the twisting is to obtain a wire of larger diameter whose fibers are parallel and oriented along the longitudinal axis of the wire. The final twist value is calculated from the same Koechlin formula given previously. Usually, the spinner selects a torsion coefficient (k) so that the yarn obtained is balanced and has no tendency to twist. For example, for cotton, it will be possible to have a torsion coefficient of between 75 <k <165, depending on the length of the fibers and the use (warp, weft, hosiery, etc.).

Applying a much greater torsion value than that usually used, for example four times higher, to achieve a torsion coefficient k greater than 400 and at least between 200 and 600 approximately, allows to have an angle β higher between the longitudinal axis of the wire and the orientation of the fibers and / or filaments. This will create instability of the wire and generate some elasticity. Nevertheless the value of this over-torsion must be studied. It must be high enough to generate elasticity, but must not be too large to avoid fiber degradation. A non-exhaustive value range for over-twisting is specified below.

Step 1

In the process of the invention, twisted twisted yarns 20, 30 are made on conventional twists capable of working on fine threads or small titles. Indeed, if the over-twisted yarn is large, especially greater than about 100 tex, the twist will be only superficial and will not reach the fibers in the heart of the yarn. The torsion should preferably apply to fine threads, especially less than about 100 tex, and for example son having a metric number (Nm) of 50 which equals 20 tex. Of course, these values are not limiting and are only mentioned by way of example.

Thanks to the tests carried out, it turned out that a torsion coefficient k of 425 would be a good compromise and would give good elasticity. For a torsion coefficient k of this value, a twist of 2100tr / m is obtained for a twisted yarn at two ends, each of Nm50 is 20 tex, to finally obtain a thread of Nm 25 or 40tex, and a twist of 1750tr. / m for a twisted yarn with three ends each of Nm50 to finally obtain a thread of Nm16 or 60 tex. This torsion can correspond to the saturating torsion Ts which is the optimal torsion (cf. Fig. 3 ) or approaching it. Of course for some specific uses, one may have to use different values while wanting to keep some elasticity. The values mentioned above are not limiting and may vary depending on the title of the wire or the material used, or even depending on the application with a wire having the same or similar characteristics.

2nd step

At the end of step 1, the over-twisted base yarns are nervous and tend to twist. In order to be able to handle them and to work them during the following operations, the over-torsion of the basic threads 20, 30 is fixed by any known method. For example, for cotton fibers, a steaming method will be chosen in an autoclave at a temperature of 90 ° C. for a determined time equal, for example, to 20 minutes. Of course, these values are not limiting and are only mentioned by way of example. Depending on the nature of the fibers and / or filaments 40 that make up the base yarns 20 and 30, it will be possible to choose a different vaporization time, a superheated steam, or another known method of fixing, such as, for example, a heat-setting process, a chemical process, etc.

Step 3

At the end of step 2, when the over-twist of the base wires is fixed, they are assembled by a braiding process to make a braided string.

The principle of manufacturing an ordinary plaited twine 1 according to the prior art, illustrated by the figures 1 and 4 , based on the fact that the basic son 2 and 3 must be at most parallel to the longitudinal axis A of the twine 1 braided, that is to say that they are close to the longitudinal axis A of the string 1 and oriented towards this axis A. In this case, a so-called tight or closed braided string 1 is obtained, in which the basic threads 2, 3 each form a low angle α and in particular less than 30 ° with the longitudinal axis A. The orientation of the basic yarns 2, 3 within the braided string 1 is due in part to the number of crosses per centimeter of braid and the braiding direction. The greater the number of crossings per centimeter, the more the braid is said to be tight or closed. In the conventional braiding process, the spindles of the braiding machine being clockwise are equipped with S-shaped bobbins 3 and the counter-clockwise bobbins are equipped with Z-twisted yarn bobbins 2. The braided string 1 obtained by the method classic has little or no elasticity.

In the process of the invention and with reference to figure 2 the arrangement of the base yarns 20 and 30 is reversed to obtain an elastic braided string. Sur-twisted S-wire bobbins are used to equip the counterclockwise spindles and overrun Z-wire spools to equip the clockwise spindles. It has been found that braiding the basic threads 20, 30 in the opposite direction of a conventional braid makes it possible to obtain a so-called loose or open braided string, when it is in the free state, it is ie without traction. The base yarns 20, 30 have a tendency to deviate from the longitudinal axis A of the braided twine and to orient towards an axis perpendicular to this axis, forming an angle α with the longitudinal axis A braided twine 10 greater than that of a conventional braided twine, for example beyond 30 ° and between 30 ° and 90 °. This phenomenon is visible on Figures 4 and 5 which make it possible to compare the same braided string by a traditional braiding process at the place and by the process of the invention in reverse. By the same string, we mean the same nature of base son, the same value of torsion, the same speed of braiding, the same number of crosses per centimeter, the same speed of traction of the braid. Only changes the meaning of braiding. The orientation of the base yarns 20, 30 within the braided twine is due in part to the number of crosses per centimeter of braid and braiding direction. The lower the number of crossings per centimeter, the more the braid is said to be relaxed or open. It has been found that braiding in the opposite direction gives a great elasticity to the braided string obtained. In addition, the fact of combining this direction of inverted braiding with an over-twist of the base yarns 20, 30 will add additional elasticity to the braided string obtained according to the invention.

When using a traditional braided string 1 (cf. Fig. 1 and 4 ), when one will apply a tensile force in the longitudinal axis A, the almost parallel orientation of the basic son 2 and 3 in the case of a conventional braided string 1 allows only little movement from where a low elasticity or even zero. Conversely, in the invention (cf. Fig. 2 and 5 ), the base wires 20 and 30 forming a large angle α with the longitudinal axis A of the braided string 10, the traction force in the longitudinal axis A will bring about a reorganization and parallelization of the base wires 20, 30 relative to the longitudinal axis A, combined with a parallelization of the fibers and / or filaments 40 with respect to this longitudinal axis A. At the moment of the removal of the tensile force, the base yarns 20 and 30 and the fibers and / or filaments 40 will tend to regain their preferred orientation, that given by the over-torsion for the fibers and / or filaments 40 and that given by the inverted braiding, resulting in a high elasticity, which can reach at least between 20% and 150% elongation at break and for example 100% elongation.

The braiding angle or the number of centimeter crossings can be varied while maintaining the elasticity characteristics of the braided twine obtained.

Additional elasticity can be achieved by releasing the over-twisting of the basic yarns 20, 30. Depending on the needs of the end user, this release may be revealed at the end of the process or during use (see example given below).

Possibilities of industrial application:

The example given below makes it possible to illustrate the method of the invention and its interest. It relates to a very specific application in the food industry for which the disadvantages associated with the use of the elastic gimped twine have already been exposed in the prior art. To overcome these drawbacks, a cotton string made according to the manufacturing method of the invention will be used.

In said example, base yarns made of twisted cotton fibers are used at two ends of Nm50 each with an over-twist of 2100 rpm.

Half of the base wires are applied with an S-twist and at the other half with Z-over-torsion.

The over-torsion is fixed on all of the base wires with steam at 90 ° C. in an autoclave for 20 minutes.

To obtain a string with a final fineness of between 2 <Nm <1.6, eight bobbins of basic thread are used, of which four bobbins are equipped with base wire previously prepared in S and four other bobbins are equipped with basic thread. previously prepared in Z.

Braided basic threads are then assembled on a conventional small-diameter braiding machine with a capacity of sixteen reels, thus provided with sixteen spindles. One spindle out of two is used. The four S-coils are installed on the spindles of the braiding machine which rotate counter-clockwise and the four Z-coils are installed on the spindles in a clockwise direction - cf. fig.2 and 5 .

In this example, the braided twine thus obtained has a natural elasticity of 120%, in particular allowing it to be used on automatic machines to tie the pieces of meat. This string has a good cohesion and can be cut without fray. The ends can be knotted easily by hand or by automatic machine. When the string is wrapped around the piece of meat, she marries and firmly holds the piece of meat without cutting it. When cooking the piece of meat, the water vapor present in the oven releases the remaining voltage contained in the over-twisted base wires 20, 30. The string 10 retracts and thus accompanies the narrowing of the piece of meat. At the end of cooking, the string 10 loses its nervousness, so its elasticity. When cut, it behaves like ordinary string without elasticity and causes no splashing.

It is clear from this description that the invention achieves the goals. The present invention is not limited to the embodiment described but extends to any modification and variation obvious to a person skilled in the art while remaining within the scope of protection defined in the appended claims. Similarly, the applications of the invention are multiple and not limited to the field of the food industry.

Claims (11)

1. Method for producing an elastic string (10) or similar, from an assembly of at least two core yarns (20, 30) made of fibers and/or filaments (40), characterized in that one applies an overtwist in a direction S to a first core yarn (20) and an overtwist in the other direction Z to a second core yarn (30), so that the fibers and/or filaments (40) form an angle β comprised between 30° and 90° with the longitudinal axis of said first core yam (20) and of said second core yam (30), one fixes the overtwist of said core yarns (20, 30) in order to stabilize them, on assembles said overtwisted core yarns by means of a braiding process to form said string (10) so that, when said string is in the free state without traction, said overtwisted core yarns tend to move away from the longitudinal axis (A) of the string and to align in the direction of an axis perpendicular to the longitudinal axis (A) of the string, forming an angle α with the longitudinal axis (A) of the string (10) comprised between 30° and 90°.
2. Process according to claim 1, characterized in that core yarns with a relatively low count are used, comprised at least between Nm 150 and Nm17 (i. e. between 6 tex and 60 tex).
3. Process according to any of the previous claims, characterized in that in the formula defining the torsion: T = k√/Nm, where T̅ is the value of the torsion in turns/m and Nm is the metric count of the yarn, one chooses a high torsion coefficient k comprised at least between 200 and 600 to obtain an overtwist value with which the fibers and/or filaments (40) form said angle β.
4. Process according to any of the previous claims, in which more than two core yarns (20, 30) are used to produce said string, characterized in that one applies an overtwist in a direction S to one part of the core yarns and an overtwist in the other direction Z to the other part of the core yarns.
5. Process according to claim 4, characterized in that an even number of core yarns is used and separated in two equal parts.
6. Process according to any of the previous claims, characterized in that the overtwist on said core yarns is fixed by means of a steaming process.
7. Process according to any of the previous claims, characterized in that at least four core yarns (20, 30) are used.
8. Process according to claim 1, characterized in that one uses a braiding machine and one arranges said core yarns (20) overtwisted in a direction S on the spindles of the braiding machine moving in the counter-clockwise direction and the core yarns (30) overtwisted in the other direction Z on the spindles of the braiding machine moving in the clockwise direction.
9. Process according to claim 8, characterized in that one uses a braiding machine having a number of spindles higher than the number of core yarns (20, 30) to be assembled and in that one arranges said core yarns on at least every second spindle.
10. Elastic string (10) obtained by the manufacturing process according to at least claim 7, characterized in that it comprises a braided assembly of at least four core yarns (20, 30) made of fibers and/or filaments (40), two first core yarns (20) having an overtwist in a direction S and two second core yarns (30) having an overtwist in the other direction Z, the fibers and/or filaments (40) of said core yarns (20, 30) forming an angle (β) comprised at least between 30° and 90° with the longitudinal axis of every core yarn; and said core yarns (20, 30) moving away from the longitudinal axis (A) of the braided string (10) and aligning in the direction of an axis perpendicular to said longitudinal axis (A) of the string, forming an angle α with the longitudinal axis (A) of the string (10) comprised between 30° and 90°.
11. String according to claim 10, characterized in that its elongation at break is comprised at least between 20% and 150%.

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