EP0500480A1 - Heat set plied yarn made from synthetic monofilaments - Google Patents

Abstract

Twisted yarn of monofilaments for applications such as, for example, use as reinforcement in tyres, for papermaking machine junction felts, tarpaulin support, knitting, braiding or other textile operations, consisting of at least two monofilaments made of synthetic material with a count of at least 20 tex, assembled, twisted and heat-set and practically free from twist stress. The synthetic material is preferably based on polyamide or polyester. Process for the manufacture of twisted yarn.

Description

The present invention relates to a thermofixed ply produced from monofilaments of synthetic material and a method of manufacturing said ply.

A monofilament is by definition a continuous thread made up of a single filament. It is generally used as it is, for example, as a horsehair or a brush, in textile applications such as weaving or knitting of technical fabrics or knits, in the paper industry, for example, as felt loops at the junction of a machine. paper, etc. It can also be used in the form of cords in textile applications such as weaving or knitting of technical fabrics or knits (for example wet felt needling base), in elastomer reinforcement applications ( for example tire reinforcement) etc ...

A cable is defined as the product resulting from the assembly and twisting of two or more twists of monofilaments; the twist being defined as the product, hitherto an intermediate product, resulting from the assembly and twisting of two or more monofilaments. In some cases the intermediate ply may consist of a single filament to which a twist has been applied.

The manufacture of a monofilament cable requires several successive operations, in particular the assembly and twisting in one direction (S for example) of the monofilaments then the assembly and twisting in the opposite direction (Z in this case) of several twists , which gives the cable. The opposite twists for the twisted and the cabled are intended to create a mechanical blocking of the cabled by opposition and balancing of the untwisting forces. However, this mechanical blockage leaves the cable a certain nervousness; there is a twisting of the cable in the free state, which hinders its transformation for example into fabrics or knits. To overcome this nervousness, it is sometimes necessary to apply significant tensions, which leads to work outside the elastic limits of the material, at the risk of damaging it.

On the economic level, the realization of these cables being carried out in several operations, it requires much more added value and a significant investment in material. On the other hand, in the case of coated cables such as those used for pneumatic, paper, coated fabrics and which are coated with a substance based on resorcinol formaldehyde, silicone or other products with rapid adhesion in order to promote adhesion, flow or any other adhesion, the coating operation currently requires a resumption of cables in additional installations hence an additional investment.

To reduce the number of operations necessary for the manufacture of cables, one could consider replacing them with plies and thus having a single twisting step. However, in this case, the antagonistic effect of the reverse twists cannot be used to obtain a relatively inert product or at least very little nervous. In this case it would be necessary to apply an overvoltage in order to work beyond the elastic limits, but there is then a significant risk of deterioration of the material, which means that this method cannot be adopted.

The present invention aims to provide a solution to the above problems.

It relates to a twisted monofilament for applications such as technical textile use, reinforcements of elastomers, paper industry, etc., characterized in that it consists of at least two monofilaments of synthetic material having a title greater than or equal to 20 tex, assembled, twisted and heat-fixed, and that it is practically free of twisting stress.

The synthetic materials which are suitable are all those usually used in the manufacture of monofilaments and in particular polyesters and polyamides in the form of homopolymers, copolymers or mixtures of polymers, where appropriate.

The number of monofilaments is not limited, it depends on the characteristics desired for the product produced. However in general this number is between two and nine.

The title of each monofilament depends on the use for which the twist is intended. However, the titer is preferably between 20 and 500 tex.

The twisting twist takes the current values in this type of operation, which are to a large extent a function of the unit strength and the number of unit monofilaments.

The ply is thermofixed under the conditions defined in the manufacturing process claimed below.

Free from internal stresses, the ply obtained having undergone changes in orientation during the heat setting will not show any twisting or separation of the strands between them when it is subjected to shear or pressure.

• - assemblage d'au moins deux monofilaments en matière synthétique, orientés et peu ou pas relaxés,
• - retordage de l'assemblé à la valeur désirée sous application d'une contrainte de tension supérieure à la contrainte limite d'élasticité,
• - fixation thermique de la torsion maintenue bloquée et simultanément relaxation du retors, la température de fixation étant supérieure au passé thermique de la matière,
• - réception du retors fixé et relaxé sur tout support approprié.

The present invention also relates to a method for manufacturing the above twist. It is a process for the manufacture of a twisted monofilament, thermofixed and practically free of twisting stress, characterized by the following steps:

• - assembly of at least two synthetic monofilaments, oriented and little or not relaxed,
• - twisting of the assembly to the desired value under application of a tensile stress greater than the elastic limit stress,
• - thermal fixation of the torsion kept blocked and simultaneous relaxation of the plied, the fixing temperature being higher than the thermal past of the material,
• - reception of the twisted set and relaxed on any appropriate support.

The starting monofilaments are produced according to a conventional spinning, stretching in several phases, relaxation process; however, the relaxation rate is lower than that usually practiced. Thus, when the monofilaments are based on polyamide the relaxation rate is advantageously between 0% and 6% instead of 0% to 12%, values usually practiced. The dynamometric characteristics are those common for this type of product and depend on the material. For polyamide 66, the elongation at break of the starting monofilaments is advantageously between 10% and 20%. Given the rate of relaxation, the material is in a moderately relaxed state, slightly repelotected macromolecules.

The assembly of two or more strands is carried out in a known manner continuously; discontinuously, it will be necessary to take the necessary precautions to obtain an assembly with regular thread tension and calculated so as not to generate a winding or twisting fault.

Twisting will be done from these monofilaments assembled in a single operation on an appropriate machine.

For the twisting step, the assembly is placed for example in a single or double twist twisting pot where it receives the desired twist.

During this operation, the assembly is subjected to a tensile stress greater than the elastic limit stress, therefore it undergoes a slight deformation comparable to a further stretching, however with the molecules oriented in the twisted direction. . At this level the product remains very nervous because it is subjected to an internal stress of detorsion.

In order to avoid untwisting, provision is made to block the torsion as soon as it leaves the twisting zone and during the entire thermal fixing step which takes place in a fixing zone following the twisting zone. The fixing zone includes a heat treatment oven and it is advantageously delimited by two capstans: an entry capstan (which also marks the exit from the twisting zone) calling the plies at constant speed while keeping torsion blocked, a exit capstan rotating at a speed lower than the entry speed, thus allowing the relaxation of the plied. The heat treatment at a temperature higher than the thermal past of the material, with the possibility of relaxation will fix the said material by repelotonnage of the molecular chains with the internal orientation acquired during the twisting, conferring on the product a stability causing it to lose most or all of it. , his nervousness.

The reception of the twisted is done for example on a reel with parallel crossing.

According to a variant of the invention, an additional step of surface treatment, for example coating, is integrated between the twisting and the fixing. For this it is necessary to keep the twisted blocked during this operation which can be achieved by means of an additional capstan.

The process is carried out at the usual wiring speeds, that is to say generally between 20 and 50 m / min approximately.

• - propriétés mécaniques équivalentes voire supérieures à celles d'un câble de même titre,
• - plus grande régularité géométrique en particulier absence de l'effet noueux que l'on trouve sur le câble,
• - plus grande souplesse qu'un monofilament ou qu'un câble de même titre,
• - vrillage très faible, voire nul, produit plus inerte.

The twist according to the invention capable of replacing cables or in some cases monofilaments used in isolation has many advantages:

• - mechanical properties equivalent to or even superior to those of a cable of the same grade,
• - greater geometric regularity, in particular the absence of the knotty effect found on the cable,
• - greater flexibility than a monofilament or a cable of the same title,
• - very weak twisting, even zero, more inert product.

The method is economically advantageous in that it allows the elimination of a twisting step. In addition, when desired it allows the continuous integration of an additional step such as coating, which until now was carried out discontinuously and required a cable recovery.

• - tissu technique nécessitant une stabilité dimensionnelle, le retors étant ou non enduit,
• - applications pneumatiques, avec retors enduit,
• - feutres de jonction pour tapis de machine à papier. Dans cette application, le retors de l'invention permet un bon positionnement du feutre autour du jonc de jonction pendant le tissage grâce à ses caractéristiques de souplesse comparable au câblé et sa régularité de section comparable à un monofilament nécessitant une bonne stabilité du retors,
• - toile de formation en papeterie par substitution des monofilaments,
• - support pour bâche,
• - tricotage, tressage, ou autres opérations textiles.

The plied according to the present invention finds many uses, in general it is used for any industrial textile application requiring the presence of cable or plied with a title greater than 20 tex, for example:

• - technical fabric requiring dimensional stability, the ply being or not coated,
• - pneumatic applications, with plied ply,
• - junction felts for paper machine mats. In this application, the twist of the invention allows good positioning of the felt around the junction rod during weaving thanks to its characteristics of flexibility comparable to cord and its regularity of section comparable to a monofilament requiring good stability of the twist,
• - training cloth in stationery by substitution of monofilaments,
• - tarpaulin support,
• - knitting, braiding, or other textile operations.

However, the invention will be better understood with the aid of the examples below, given by way of illustration and not limitation.

Example 1

The standard wired control product which the twist according to the invention proposes to replace is produced from shrinked polyamide 66 monofilaments, according to the procedure described below.

A polyamide 66 with a melting point 256 ° C. of a viscosity index (IV) of 126, measured according to international standard ISO 307-1977, is extruded under the following conditions:

After extrusion, the monofilaments are cooled in water to 35 ° C, then undergo a series of three phases of hot drawing:

1st stretch

• - stretch rate: 3.6
• - stretching temperature (by passing through a water tank): 95 ° C

2nd stretch

• - cumulative stretch rate: 4.5
• - stretching temperature

(by passage in a hot oven): 160 ° C

After stretching the monofilaments are subjected to relaxation and thermal fixation, relaxation rate 12%, fixing temperature 215 ° C (passage through a hot air oven). The monofilaments are finally wound, winding speed: 180 m / min, weight of the windings: 2 kg.

The monofilaments obtained have the following characteristics:

Three of these monofilaments are wired to form a product of about 0.46 mm in diameter, it is a 1-strand x 3-strand wiring, each unitary strand having undergone a primary twist Z240 rpm then the three strands are assembled and the assembly wired by a reverse twist S250 rpm. The cable obtained has the following characteristics:

Twist is measured by the method described in French Standard G07 314, it corresponds to the number of loops formed after having unrolled 1 meter of cable or twists and joined the ends.

This cable can be used in applications such as a base for stationery felts and in some cases as a weft on the loom to form the felt joining loop, this loop then being in the direction of operation on a paper machine.

A twist according to the invention is then produced for comparison.

The monofilaments are manufactured by the same process as the control with the same parameters, except for the relaxation rate which is 6% instead of 12% and the assembly by three in this case.

Monofilaments have the following characteristics:

From the three threads as above, a twist according to the invention is produced by the method according to the invention.

A modified twisting machine is used for the implementation of the method, it comprises in particular a thermal fixing oven, a first call capstan located upstream of the oven (leaving the twisting area) and a second capstan located downstream from the oven (leaving the fixing area).

The spool of triwires is placed in the twisting pot of the machine where the assembly receives a S240 twist. Twisting is carried out with the application of a tension of 400 CN, ie a stress of 2.2 CN / tex, greater than the elastic limit stress. Continuous, twist kept blocked by the capstans, the plied is subjected to a thermal fixing by passage in the oven at the temperature of 200 ° C, higher than the thermal past of the material, with application of a relaxation rate of 8% . The speed of the upstream capstan is 21.6 m / min, that of the downstream capstan 20 m / min, that is to say identical to that of production of the control cable, hence no loss of productivity.

The twisted is received on a spool with parallel cross winding, winding weight 2 kg. The plied has the following characteristics:

It is noted that the dynamometric characteristics of the plied are practically identical (slightly superior) to those of the control cable. On the other hand, its nervousness is clearly reduced: twisting 1 turn / meter instead of 10 turns / meter, which represents a significant improvement. The plied advantageously replaces the control cable in the aforementioned applications, moreover its shorter manufacturing process, since there is no stage of application of the primary torsion, brings a significant economic gain.

Example 2

The twist according to example 1 is used for the production of joining loops on felt at the junction of the paper machine, press section. This junction is made by a loop at each end of the felt favoring its mounting during its change, for this a rod is introduced between the loops, thus binding the felt.

These loops are commonly made of monofilament. However, monofilament is a rigid product which tends to tilt during the shaping of the loop. These cables are far too nervous products and present many difficulties in this application.

The thermofixed ply according to the invention replaces a 200 tex monofilament, it provides the characteristics of flexibility and longitudinal regularity in section.

This homogeneity of section will favor the characteristics sought in felts, namely dryness, compressibility. The fact that this twist has a non-round section promotes blocking of the meshes when making the base.

Example 3

It relates to the production of a coated twist usable in applications such as anti-sal technical fabric from re.

It is carried out under the same conditions as those described in Example 1, but with the introduction of a coating step between the twisting and the thermal fixing. The coating material consists of a rou water lapping.

The product to be applied is a polymerizable silicone with rapid polymerization in the form of a liquid.

The heat treatment oven is used both for the thermofixing of the plied (fixing of the twist) and the polymerization of the coating.

The speed of the process is between 20 and 50 m / min.

Claims (12)

1. Twisted monofilaments for applications such as technical textile jobs, elastomer reinforcements, paper industry, etc. characterized in that it consists of at least two monofilaments of synthetic material with a title at least equal to 20 tex assembled , twisted and thermofixed, and that it is practically free of twisting stress. 2. Twisted according to claim 1, characterized in that it has a twist less than two turns per meter and preferably at most equal to one turn per meter. 3. Twisted according to one of claims 1 or 2, characterized in that the synthetic material is based on polyester. 4. Twisted according to one of claims 1 to 3, characterized in that the synthetic material is based on polyamide. 5. Twisted according to claim 4, characterized in that the synthetic material is polyamide 66. 6. Twists according to claim 4, characterized in that the synthetic material is a copolyamide 66/6. 7. A process for the manufacture of a twisted monofilament according to claims 1 to 6, heat-set and practically free of twisting stress, characterized by the following steps: - assembly of at least two synthetic monofilaments, oriented and little or not relaxed, - twisting of the assembly to the desired value under application of a tensile stress greater than the elastic limit stress, - thermal fixation of the torsion kept blocked and simultaneous relaxation of the plied, the fixing temperature being higher than the thermal past of the material, - reception of the twisted set and relaxed on any appropriate support. 8. Method according to claim 7, characterized in that the starting monofilaments are based on polyamide and are obtained by spinning, stretching, relaxation with a relaxation rate of between 2% and 8%. 9. Method according to one of claims 7 or 8 characterized in that the twisting and thermal fixing operations are carried out continuously by passing through consecutive areas on a suitable machine. 10. Method according to one of claims 7 to 9 characterized in that the blocking of the torsion during the fixing step is carried out by two capstans call respectively located at the entrance and at the exit of the zone fixing. 11. Method according to one of claims 7 to 10 characterized in that an additional step of surface treatment is integrated between the twisting and fixing steps. 12. Method according to claim 11 characterized in that the surface treatment is a coating.