EP0986658B1 - Thermotropic aromatic polyester(amide) monofilament - Google Patents

Description

The present invention relates to polyester (amide) aromatic thermotropic fibers, more specifically to the monofilaments of such polymers, as well as to the processes for obtaining such monofilaments.

Elaboration from thermotropic aromatic polyester (amide) of conventional fibers multiftlamentary made up of a large number of filaments of small elementary diameter (typically around 20 to 30 µm), or of large diameter unitary monofilaments (at least less than 40 µm), by "melt-spinning" of the polymer generally followed of a so-called post-polycondensation heat treatment is a known technique.

International application WO92 / 12018 (equivalent patents EP-B-517 870 and US 5,427,165) describes in particular reinforcement assemblies intended to replace steel cables in tire casings. these assemblies being made up of monofilaments in liquid crystal organic polymers with very high mechanical properties, especially in aromatic polyester. To obtain these aromatic polyester monofilaments, extrudes the molten polymer at 340 ° C through the capillary of a die whose diameter is 800 µm and whose temperature is 270 ° C; the liquid jet leaving the die is stretched in air (drawing ratio equal to approximately 20), then solidified by passing through a quenching zone thermal. The raw spinning monofilament thus obtained is taken from a winding at a speed of 590 m / min, to then be subjected to the heat treatment of postpolycondensation on the receiving coil: this postpolycondensation phase particularly long on this type of polymer (several hours) in fact implies that the treatment is carried out on a reel, generally in an oven, and not on a moving single-wire continuous through this oven. After heat treatment, the monofilaments have a diameter about 180 µm the following mechanical properties: initial modulus of 4300 cN / tex, 2.5% elongation at break and 130 cN / tex toughness. Due to the liquid crystal character of the starting polymer, the monofilaments already have in the raw spinning state a module very high initial, greater than 4000 cN / tex, postpolycondensation heat treatment being essentially intended to increase the toughness of the spun products.

However, a significant drawback of the raw spinning monofilaments described above is that they have the particularity of contracting hot. This property, probably linked to a release of "frozen" constraints during spinning, makes it difficult to implement the subsequent post-polycondensation phase and it is detrimental to the quality of heat treated monofilaments derived therefrom, as explained below.

It turns out that if you don't allow the monofilaments to contract freely during their heat treatment, on their support coil, the latter will develop very high tensions which can lead to their partial damage, or even to a Self-breaking. In addition, risks of interfilament bonding exist between turns adjacent or superimposed, risks due to the combined action of the contraction tension and the temperature ; such bonding, if it takes place, may prevent satisfactory subsequent unwinding of the monofilaments treated.

To limit the above risks, we have certainly tried, before the treatment of the raw monofilament spinning, rewinding them at very low speed (a few tens of m / min) to obtain tension as low as possible on the support coil; but this operation is expensive from the industrial point of view and delicate to implement when it comes to treating lengths important monofilaments. We also tried to use geometry for slicing crossed limiting the contacts between the wires, but the contraction then induces damage in flexion-compression at the contact points.

To leave instead the monofilaments the possibility of contracting freely during their treatment, we experimented with the use of specific flexible coils which contract more or less under the effect of tension (variable diameter), this avoiding operations rewinding prerequisites under very low voltage. The use of such coils, admittedly little practical and more expensive, especially reveals another major drawback of these raw spinning monofilaments: their self-compression during thermal contraction in most cases causes irreversible structural damage manifesting itself, on the products treated, by the presence of compression defects well known under the name of "kink-bands", as soon as a critical compression threshold - relatively low threshold on this type of polymer - is exceeded.

So whatever solution has been adopted, none has so far been found to be completely satisfactory with regard to the various problems posed by raw spinning monofilaments hot contracting, in particular during their postpolycondensation heat treatment.

Some of the drawbacks described above are not specific to large diameter monofilaments, and have already been described for multifilament fibers conventional in thermotropic aromatic polyester (amide).

However, all these disadvantages are generally exacerbated on monofilaments in because of their larger diameter: damage to a filament after treatment thermal may go unnoticed for example on a multifilament fiber formed of several hundred filaments, while it most often becomes unacceptable on a large diameter unitary monofilament.

The primary purpose of the invention is to overcome the aforementioned drawbacks by proposing a new monofilament in thermotropic aromatic polyester (amide) which, in the raw spinning state ("as-spun"), has the characteristic of not contracting hot.

This raw spinning monofilament verifies the following relationships: D ≥ 40; Te>45; ΔL ≥ 0,

D being its diameter (in μm), or its thickness in the case of an oblong or flattened shape, Te its toughness (in cN / tex) and ΔL its variation in length (in%) after 2 minutes at 235 ± 5 ° C under a pretension of 0.2 cN / tex.

When the monofilament of the invention is intended to reinforce plastic articles and / or rubber, in particular tire casings, D is preferably included in a range from 80 to 230 μm, more preferably from 100 to 200 μm.

Compared to the prior art thermotropic aromatic polyester (amide) monofilaments, in particular in the range from 80 to 230 μm above, the raw spinning monofilament of the invention has the advantage of having, for a given polymer and a given diameter D. a lower extension module combined with an elongation at break which is generally higher, which is an advantageous compromise. We know that in a way general, for fibers of liquid crystal origin with very high mechanical properties, such combination is favorable for better properties in flexion-compression, particularly used when plastic and / or rubber articles are to be reinforced, in particular especially tire casings; this best compromise observed on raw spinning monofilaments is kept on the heat treated monofilaments which derive from it.

Thus, preferably, the raw spinning monofilament of the invention verifies the relationships: Mi <4000;Ar> 2,

Mi being its initial modulus (in cN / tex) and Ar its elongation at break (in%).

a) fondre le polymère;

b) extruder le polymère fondu à travers une filière comportant au moins un capillaire d'extrusion;

c) en sortie du capillaire, structurer l'écoulement du polymère par étirage dans une couche de fluide gazeux, de préférence de l'air, pendant un temps ts prédéterminé;

d) au bout du temps ts, tremper thermiquement l'écoulement de polymère ainsi structuré par passage dans un liquide de trempe, de préférence de l'eau, de manière à le solidifier;

e) après l'avoir éventuellement séché, bobiner le monofilament ainsi obtenu,

   le temps ts (en secondes) étant lié au diamètre ou épaisseur D (en µm) du monofilament brut de filage par la relation (1) suivante: ts < to = 6.10-6 D2. The monofilament of the invention is obtained by a new and specific spinning process which constitutes another object of the invention, this process being characterized in that it comprises the following stages:

a) melting the polymer;

b) extruding the molten polymer through a die comprising at least one extrusion capillary;

c) at the outlet of the capillary, structure the flow of the polymer by stretching in a layer of gaseous fluid, preferably air, for a predetermined time ts;

d) at the end of the time ts, thermally quenching the flow of polymer thus structured by passage through a quenching liquid, preferably water, so as to solidify it;

e) after having possibly dried it, wind the monofilament thus obtained,

the time ts (in seconds) being linked to the diameter or thickness D (in μm) of the raw spinning monofilament by the following relation (1): ts <to = 6.10 -6 D 2 .

The raw spinning monofilament of the invention can be used as it is, or else treated thermally to obtain an aromatic polyester (amide) monofilament post-polycondensed thermotrope which constitutes another object of the invention.

The invention further relates to the use of the monofilaments of the invention, whether in the state assembly or unitary wire, for the reinforcement of plastic and / or rubber, as well as its articles themselves, in particular the rubber tablecloths intended in the manufacture of tires and these tires themselves.

The invention, as well as its advantages, will be easily understood in the light of the description and examples of embodiments which follow.

I. MEASUREMENTS AND TESTS USED I-1. Optical properties of polymers

The optical anisotropy of the polymers is tested by observing in the molten phase (i.e. above the polymer melting temperature) a drop of polymer between polarizer and analyzer crossed lines of a polarization optical microscope (Olympus type BH2), at rest that is to say in the absence of dynamic constraint.

In a known manner, if the polymer is thermotropic (i.e. liquid crystal), the above preparation is optically anisotropic, that is to say that it depolarizes light: thus placed between crossed linear polarizer and analyzer, it has a light transmission (texture more or less colorful); an optically isotropic preparation, under the same conditions observation, does not have the above depolarization property, the field of microscope remaining black.

I-2. Mechanical properties of monofilaments

In the present description, the term "monofilament" or "monofilament" means a unitary filament whose diameter or thickness (i.e. the smallest transverse dimension of its section right when it is not circular), noted D, is at least equal to 40 µm (title 1.7 tex minimum).

The above definition therefore covers both monofilaments of essentially cylindrical (ie with circular section) than oblong monofilaments, monofilaments of flattened shape, or strips or films of thickness D.

All the mechanical properties below are measured on monofilaments having been subject to pre-conditioning: "pre-conditioning" means the storage of monofilaments (after drying) for at least 24 hours, before measurement, in a standard atmosphere according to European standard DIN EN 20139 (temperature of 20 ± 2 ° C ; humidity ± 65 ± 2%).

The titer of the monofilaments is determined on at least three samples, each corresponding to a length of 50 m, by weighing this length of monofilament. The title is given in tex (weight in grams of 1000 m of monofilament - reminder: 0.111 tex equal to 1 denier).

Mechanical properties in extension (toughness, initial modulus, elongation at break) are measured in a known manner using a ZWICK GmbH & Co traction machine (Germany) type 1435 or type 1445. The monofilaments undergo traction on a initial length of 400 mm at a nominal speed of 50 mm / min. All results given are an average of 10 measurements.

The tenacity (force-breaking divided by the title) and the initial modulus are indicated in cN / tex (centinewton per tex - reminder: 1 cN / tex equal to 0.11 g / den (gram per denier)). The module initial is defined as the slope of the linear part of the Force-Elongation curve, which comes just after a standard pretension of 0.5 cN / tex. The elongation at break is indicated as a percentage.

The diameter D of the monofilaments is determined by calculation from the titer of the monofilaments and their density, according to the formula: D = 2.10 1.5 [Ti / πρ] 0.5

D being expressed in µm, Ti being the title in tex, and ρ being the density in g / cm ³ (ρ is equal to about 1.4 in the present case).

In the case of a monofilament with a non-circular cross-section, that is to say other than a monofilament of essentially cylindrical shape, the parameter D, which then represents the smallest dimension of the monofilament in a plane normal to the axis of the latter, is no longer determined by calculation but experimentally, by optical microscopy on a cross section of this monofilament, the latter being for example previously coated in a resin to facilitate cutting.

I-3. Length variation thermal test

The thermal behavior of the monofilaments is analyzed, after conditioning prior, using a test called "thermal variation test of length" whose principle is well known to those skilled in the art in the field of textile fibers.

According to this test, the thermal variation in length denoted ΔL is measured by introducing the monofilaments. under a pretension of 0.2 cN / tex, in an oven previously balanced with temperature of 235 ° C ± 5 ° C.

In practice, a known commercial device of the "Testrite" type is used (model MK3 marketed by the company Testrite). The useful sample length (without significant impact on the measurement) is 254 mm. ΔL is measured automatically by the device, using mechanical sensors, and the measurement result is read on a digital display, after 2 minutes at a temperature of 235 ° C ± 5 ° C; a positive ΔL variation corresponds to a dilation of the monofilaments, while a negative ΔL variation corresponds to a contraction of these last.

II. CONDITIONS FOR CARRYING OUT THE INVENTION II-1 Polymer

The starting polymer is any polyester or thermotropic aromatic polyester-amide which can be spun to the molten state. Such polyesters or polyester-amides called "fully aromatic" are known to those skilled in the art and have been described in a very large number of documents.

By way of example, mention may be made of patents or patent applications EP 091 253; EP 205,346; EP 267,984; EP 508,786; EP 737,707; US 3,491,180; US 4,083,829, US 4,161,470; US 4,183,895; US 4,447,592; US 4,734,240; US 4,746,694; US 5,049,295; US 5,110,896; US 5,250,654; US 5,296,542; JP 1992/333 616; JP 1996/260 242.

le rapport molaire A:B étant compris dans un domaine allant de 10:90 à 90:10. de préférence de 20:80 à 30:70.The invention is preferably implemented from a specific thermotropic aromatic polyester: this polymer consists essentially of repeating units (A) of 6-oxy-2-naphthoyl and (B) of 4-oxybenzoyl:

the A: B molar ratio being in a range from 10:90 to 90:10. preferably from 20:80 to 30:70.

Such a polymer, sold in particular by the company Hoechst Celanese under the name of Vectra, has been described in US 4,161,470 and can be obtained by copolymerization of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, these two acids possibly being substituted. It has, in known manner, an excellent compromise of properties in terms of thermal resistance, chemical resistance, ease of implementation and suitability for spinning, in particular due to a relatively low melting point (hereinafter denoted Tm). A polymer of this type - Vectra type 900 or 950 with molar ratio A: B equal to 27:73 - is widely known for conventional multifilament fibers (see for example J. Text. Inst., 1990, 81 No 4. pp. 561-574) and was also used for obtaining monofilaments of the prior art described in the aforementioned application WO92 / 12018.

II-2. Spinning

The starting polymer, for example in the form of granules or powder, is dried under vacuum then introduced into an extruder having one or more heating zones different. As with spinning conventional multifilament fibers, the temperatures and the residence times imposed in these different zones are such that they allow complete melting of the polymer, rotation and screw torque conditions stable extrusion offering a regular supply to the spinning pump, and finally to avoid degradation of the polymer in the extruder.

At the extruder outlet, the molten polymer, then at the temperature denoted Tx (temperature of extruder outlet). is transferred to a spinning pump which feeds a preceding die a filter.

The die may include a single extrusion capillary or more depending on whether one wishes spinning a single monofilament or several monofilaments in parallel; we will consider below the case of a die with a single capillary.

The diameter of the capillary, noted "d", is not a critical parameter of the process: it can vary in a wide range, for example from 200 to 1500 µm, or even more. according to the diameter D targeted. As indicated previously, the invention also relates to the cases where the monofilaments have a cross section other than circular, such a shape being obtainable by example by modifying the cross section of the extrusion capillary; for such monofilaments, the parameter d then represents the smallest transverse dimension of the capillary, i.e. its smallest dimension measured in a plane normal to the direction flow of the polymer.

Preferably, the die temperature denoted Tf is lower than the temperature Tm (polymer melting temperature).

At the outlet of the die and of the extrusion capillary, a liquid extrudate is therefore obtained. (flow of polymer) consisting of an elementary liquid vein having the shape of a still liquid monofilament. This liquid polymer vein is then structured. oriented by stretching (see below FEF spinning factor) in a fluid layer gas, for a predetermined time ts, this before entering a liquid zone of thermal quenching.

By convention, the term structuring duration denoted ts means the total duration of passage from the flow of polymer in the layer of gaseous fluid, whatever the profile or gradient drawing the flow in this layer of gaseous fluid.

The layer of gaseous fluid is preferably air, the thickness of which, denoted Ag, can vary by example from a few centimeters to several meters, depending on the specific conditions of placing of the invention, in particular according to the durations ts referred to. By thickness Ag is meant from the layer of gaseous fluid the distance between the outlet of the die and the inlet of the zone thermal quenching liquid. Preferably, the temperature denoted Tc of the fluid layer gas is notably lower than Tf, Tc being generally close to the temperature ambient (about 20 ° C).

According to the invention, the structuring time ts (in seconds) is linked to the diameter D (in μm) of the raw spinning monofilament by the following relation (1): ts <to = 6.10 -6 D 2 .

A structuring time ts lower than the critical value to above is a condition necessary to guarantee, whatever the diameter D aimed, the obtaining of a raw monofilament of spinning not contracting hot (i.e. showing a variation ΔL ≥ 0 on the variation test length).

Preferably, the following relation (2) is verified: 1.5.10 -6 D 2 <ts <6.10 -6 D 2 .

It is indeed desirable that the structuring times ts are not too short, if one wants to obtain monofilaments with sufficient strength to be able to claim reinforcement of rubber articles such as tires.

It has been observed that the implementation of the process of the invention in accordance with relation (2) above, for spinning monofilaments of diameter D from 80 to 230 µm, more preferably from 100 to 200 μm, in particular from the polymer with repeating units A and B previously defined, was particularly favorable for obtaining an initial module Mi between 2500 and 4000 cN / tex, more preferably at least equal to 3000 cN / tex and less than 4000 cN / tex. For such preferential conditions, when the process is implemented work to obtain monofilaments with a circular section of diameter from 100 to 200 µm, we in addition, the following conditions are more preferably used: the spinning speed (see below Vf) is within a range of 500 to 1000 m / min and the thickness of the layer of gaseous fluid (Ag) is chosen to be greater than 0.50 meters and less than 2.0 meters.

At the end of time ts, the flow of polymer thus structured, oriented, enters the zone thermal quenching liquid where, in contact with the liquid agent, it solidifies and thus forms a monofilament. Preferably, the liquid thermal quenching agent is water and its temperature noted Tl is preferably lower than ambient temperature, for example in the range of 10 to 15 ° C.

For this liquid thermal quenching operation, simple means can be used consisting for example of a bath containing the quenching liquid and through which flows the monofilament in formation. The liquid quenching time is not a critical parameter and can vary for example from a few milliseconds to a few tenths of a second, or even a few seconds, according to the specific conditions for implementing the invention.

It is generally at the outlet of the liquid thermal quenching zone that the monofilament is taken up on a drive device, for example on a call slab, at a speed determined called spinning speed and denoted Vf. The relationship between Vf and the extrusion speed Ve of the solution through the chain, defines what is known in a known way the factor drawing to spinning (abbreviated as FEF = Vf / Ve).

Typically, the stretch factor and the spinning speed can vary within a very wide range, for example from 2 to 50 for the FEF and from 100 to 1500 m / min for Vf.

It was found that the mechanical properties of the monofilaments were very little influenced by the spinning factor for ranges as large as those indicated above, whereas they proved to be particularly sensitive to the duration of structuring ts before liquid thermal quenching. In other words, and unexpectedly, the properties obtained are essentially dependent, at given diameter D, on the duration of structuring and not the amplitude of deformation imposed during stretching.

The raw spinning monofilament thus obtained is then wound at speed Vf, on a spool reception. It can optionally be dried before winding, for example by scrolling continuous on heating rollers, or else be wound in the wet state and then dried on a reel. for example in ambient air or at a higher temperature in an oven. before a pre-conditioning for the measurement of its thermal and mechanical properties.

As a general rule, the initial modulus Mi and the elongation at break Ar of the monofilament of the invention can be largely modulated by the choice of the starting polymer and spinning conditions, the initial module in particular being all the higher as the rigidity of the polymer is greater (eg use of thermotropic polyester amides).

Preferably, for better performance in flexion-compression, the raw spinning monofilament of the invention verifies the following relationships: Mi <4000;Ar> 2,

Mi being its initial modulus (in cN / tex) and Ar its elongation at break (in%).

It was further observed that an ΔL value ≥ 0.2 was most often associated with an even higher elongation at break; thus, more preferably, the following relationships are both verified: ΔL ≥ 0.2; Ar ≥ 2.5.

When the monofilaments according to the invention are intended for reinforcing articles in rubber, especially of tires, their toughness in the raw state of spinning is preferably greater than 55 cN / tex, more preferably greater than 65 cN / tex; their initial module, at the raw spinning state is preferably between 2500 and 4000 cN / tex, more preferably at least equal to 3000 cN / tex and less than 4000 cN / tex.

II-3. Postpolycondensation treatment

Post-polycondensation heat treatment, after spinning, essentially allows increase the toughness available on monofilaments, by increasing the degree of polymerization of the polymer; in general, the more advanced the heat treatment, the higher the toughness obtained after treatment. Monofilaments are thus obtained in thermotropic aromatic polyester (amide) called postpolycondensed, which are directly derived from raw monofilament yarns described above.

For this treatment, the coils of raw spinning monofilaments are treated in ovens in known manner, at high temperatures, under vacuum or under inert gas, for example under flow nitrogen, usually for several hours. The conditions of this processing postpolycondensation, which in known manner varies depending on the nature of the polymer used, are similar to those used for conventional fibers multifilament. Special treatment conditions have been described, for example in US 4,161,470 for these conventional fibers, and in application WO92 / 12018 above for monofilaments with a diameter of 180 µm: such conditions are also given in the exemplary embodiments which follow.

Preferably, the post-polycondensed thermotropic aromatic polyester (amide) monofilament derived from the raw spinning monofilaments of the invention, of diameter D at least equal to 40 μm, verifies the following relationships: Mi <4000;Ar>2;Te> 100,

Mi being its initial modulus (in cN / tex), Ar its elongation at break (in%), and Te sa tenacity (in cN / tex). More preferably, its Mi module is between 2500 and 4000 cN / tex, more preferably still at least equal to 3000 cN / tex and less than 4000 cN / tex ; its elongation at break Ar is preferably at least equal to 2.5.

The raw spinning monofilaments of the invention such as those in the post-polycondensed state which are derived, can be used in various applications, in particular for manufacturing or reinforcement of various articles, in particular plastic articles and / or rubber, for example belts, hoses, tire casings.

When they are used to reinforce plastic and / or rubber articles, in particular in the form of cables, they preferably verify the following relation (D in μm): 80 ≤ D ≤ 230.

A diameter at least equal to 80 µm is preferred in view of the wiring costs (need to limit the number of wires in the cables, for a given breaking strength), while a diameter greater than 230 µm is generally to be avoided to limit damage in bending-compression (disadvantage of large diameters with a small radius of curvature). In addition, a diameter greater than 230 µm is hardly compatible with obtaining toughness sufficient, especially for reinforcing tires.

Even more preferably, when the monofilaments of the invention are used to reinforce tires, the following relation is obtained which is verified: 100 ≤ D ≤ 200.

III. EXAMPLES OF EMBODIMENT OF THE INVENTION Trial 1

The purpose of this test is to show the sensitivity of the properties of a polyester monofilament. thermotropic aromatic, of determined diameter D, with the duration of structuring ts.

6 examples of raw spinning monofilaments are produced, 5 of which conform to the invention (examples A-1 to E-1), and a comparative example F-1 not in accordance with the invention.

The thermotropic aromatic polyester used here is a known polymer of the Vectra A900 type, in the form of granules, marketed by the company Hoechst Celanese, consisting of recurring units (A) and (B) as defined above, according to a molar ratio A: B equal to about 27:73 (Tm equal to 280 ° C according to DSC analysis).

The extruder in which the polymer is melted includes three heating zones successive, respectively at 275 ° C, 310 ° C and 340 ° C (Tx = 340 ° C), the following spinning pump being also maintained at the temperature Tx of 340 ° C. The temperature Tf and the diameter d of the single capillary of the die are respectively equal to 270 ° C and 800 µm. The length noted "1" of the capillary is equal to twice its diameter (l / d = 2) and the angle noted α of converging preceding the entry of the capillary is equal to 8 degrees. The FEF is equal to 19.7 (Vf = 590 m / min). The spinning conditions are adjusted in a known manner, by varying the speed of the spinning pump and on the speed of extrusion through the die, so as to obtain a monofilament with a diameter D of approximately 180 μm (titer equal to approximately 34.5 tex).

At the outlet of the extrusion capillary, the flow of the polymer is structured (i.e. the liquid stream leaving the capillary) by stretching in a layer of air (room temperature 20 ° C) for a variable time ts such that the above-mentioned relation (1) (ie ts <to = 0.19 s) is verified or not.

At the end of the time ts, the flow of polymer thus structured is thermally quenched by forced passage of the monofilament under a pulley immersed in a water bath at 15 ° C; the length of submerged monofilament is approximately 10 cm, which corresponds to a time of very short but sufficient thermal quenching of approximately 10 milliseconds. At the end of the bath of water, the monofilament is taken up and wound up in several turns on a drive device consisting of a call slab, at the speed Vf indicated above of 590 m / min.

The monofilament is then taken from a reel in the wet state and allowed to dry at air for 24 hours, before conditioning for the measurement of its properties thermal and mechanical.

The structuring time ts was thus varied according to the indications in Table 1 - either 0.02 to 0.40 s - gradually increasing the thickness Ag of the air-gap from 0.2 m (eg A-1) to 3.9 m (eg F-1), successively passing through Ag values of 0.55 m (eg B-1), 0.75 m (e.g. C-1), 1.10m (e.g. D-1) and 1.60m (e.g. E-1). All wiring conditions are in compliance to the invention, with the exception of the duration ts for example F-1 which does not verify the relation (1) above (ts <to).

Table 1 also indicates the properties of the monofilaments obtained.

It can be seen that the monofilaments prepared according to the spinning process in accordance with the invention (examples A-1 to E-1) verify all of the following relationships: D ≥ 40; Te>45; ΔL ≥ 0.

Examples A-1 to D-1 further verify the following preferential relationships: Mi <4000; Ar> 2.

In addition, examples A-1 to B-1, obtained for the shortest structuring times ts, verify the following preferential relationships: ΔL ≥ 0.20; Ar ≥ 2.5.

The initial module can thus be lowered to values between 2500 and 4000 cN / tex without affecting the toughness which remains in all cases greater than 65 cN / tex.

It is noted in particular that the monofilaments B-1, C-1, D-1 and E-1 (diameter 180 μm), which are obtained according to a process verifying the above-mentioned relation (2), namely: 1.5.10 -6 D 2 (i.e. 0.049 s) <ts <6.10 -6 D 2 (i.e. 0.194 s), all have the following preferred characteristic: 3000 ≤ Mi <4000.

As for Example F-1 prepared according to a spinning process not in accordance with the invention (ts> to), it has a "hot" contraction (ΔL negative) and is therefore not in accordance with the invention: also has a particularly high initial module. greater than 4000 cN / tex, and a Ar value less than 2%.

It can therefore be seen in this test that the parameters ΔL, Mi and Ar are particularly sensitive to an increase in ts. In particular, the continuous increase in the initial module Mi with ts - and therefore with the thickness Ag of the air layer - appears rather unexpected in the extent that the skilled person could expect to observe on the contrary, for thicknesses air gap of up to several meters, a decrease in the initial module due to molecular relaxation process in the liquid crystal flow of the polymer.

On the other hand, it is noted in this test that the monofilaments in accordance with the invention have significant thermal expansion (ΔL ≥ 0.2 for all examples: ΔL ≥ 0.4 in most cases cases): advantageously, such properties may in particular authorize their winding under high tension, during spinning, before the subsequent treatment of post-polycondensation.

Trial 2

• le polyester aromatique thermotrope est un polymère connu type Rhodester CL de la société Rhône-Poulenc (Tm=305°C), issu des monomères suivants (% en mole): acide p-acétoxybenzoïque (23%), acide téréphtalique (19%), diacétate de méthylhydroquinone (39%) et acide 4-4'-diphénylétherdicarboxylique (19%);
• les trois zones de chauffage successives de l'extrudeuse sont à 330°C (Tx=330°C), la température de pompe est égale à 310°C, et la température de filière à 270°C (Tf=270°C);
• le diamètre d du capillaire de la filière est égal à 400 µm (l/d = 2 ; α = 8°), le FEF est égal à 4,9 (Vf=590 m/min).

In this test, we proceed as for test 1 above, with the following modifications:

• the thermotropic aromatic polyester is a known polymer of the Rhodester CL type from the company Rhône-Poulenc (Tm = 305 ° C), derived from the following monomers (mol%): p-acetoxybenzoic acid (23%), terephthalic acid (19%) , methyl hydroquinone diacetate (39%) and 4-4'-diphenyl etherdicarboxylic acid (19%);
• the three successive heating zones of the extruder are at 330 ° C (Tx = 330 ° C), the pump temperature is equal to 310 ° C, and the die temperature at 270 ° C (Tf = 270 ° C) ;
• the diameter d of the capillary of the die is equal to 400 μm (l / d = 2; α = 8 °), the FEF is equal to 4.9 (Vf = 590 m / min).

The structuring time ts is varied according to the indications in Table 2, increasing gradually the thickness Ag of the air-gap from 0.55 m (ex. A-2) to 4.00 m (ex. D-2), passing by Ag values of 0.80 m (eg B-2) and 2.20 m (eg C-2). All wiring conditions are in accordance with the invention with the exception of the duration ts which, for examples C-2 and D-2, does not not verify the above-mentioned relation (1) (ie ts <to = 0.19 s); for examples A-2 and B-2, the relation (2) is verified.

Table 2 also indicates the properties of the raw spinning monofilaments thus obtained.

It can be seen that the monofilaments of examples A-2 and B-2, prepared according to the process according to the invention, verify the following relationships: D ≥ 40; Te>45; ΔL ≥ 0.

These monofilaments A-2 and B-2 also verify the following preferential relationships: Mi <4000 and Ar> 2; their tenacity Te is greater than 55 cN / tex.

As for the monofilaments of variants C-2 and D-2, if they certainly have an initial Mi module significantly lower than 4000 cN / tex, simply due to the nature of the polymer used work (lower rigidity and optical anisotropy than for the polymer of test 1 above), they both show a negative ΔL variation, i.e. a hot thermal contraction at length variation thermal test; they are therefore not in accordance with the invention.

Trial 3

• le diamètre d du capillaire de la filière est de 600 µm (l/d = 2 ; α = 8°);
• l'épaisseur Ag de la couche d'air est constante et égale à 1,4 m;
• on fait varier le diamètre D du monofilament à durée de structuration ts constante (ts = 0.14 s), selon les indications du tableau 3.

In this test, we proceed as for test 2 above, with the following modifications:

• the diameter d of the capillary of the die is 600 μm (l / d = 2; α = 8 °);
• the thickness Ag of the air layer is constant and equal to 1.4 m;
• the diameter D of the monofilament is varied with a constant structuring time ts (ts = 0.14 s), according to the indications in Table 3.

The spinning speed is constant (Vf = 590 m / min); the diameter D is adjusted by 95 µm (ex. A-3) at 320 µm (eg G-3) by modifying the speed of the spinning pump in a known manner (FEF varying from approximately 3.5 to approximately 40).

All the spinning conditions are in accordance with the invention, with the exception of the duration ts which, for the 4 examples referenced A-3 to D-3, do not verify the above relation (1) (ts = 0.14 s> to for these 4 examples A-3 to D-3).

Table 3 also indicates the properties of the monofilaments obtained. Note that the monofilaments of examples E-3, F-3 and G-3, prepared according to the process in accordance with the invention (ts <to), verify all the following relationships: D ≥ 40; Te>45; ΔL ≥ 0.

These monofilaments in accordance with the invention also verify the following preferential relationships: Mi <4000 and Ar> 2; the Te is greater than 55 cN / tex for the E-3 and F-3 monofilaments.

As for the monofilaments of Examples A-3 to D-3, prepared according to a process not in accordance with the invention (ts> to), if they certainly present, as for examples C-2 and D-2 above, a initial modulus Mi less than 4000 cN / tex (polymer less rigid than for test 1), they are all characterized by a negative ΔL variation, i.e. by a hot thermal contraction at length variation thermal test: they are therefore not in accordance with the invention.

Trial 4

In this test, the monowires of Examples A-2 to D-2 above (test 2) are subjected to a postpolycondensation heat treatment.

For all starting materials, we rewind at low speed (cross-traning about 30 °) on flexible coils likely to retract more or less under the effect thermal contraction of the monofilaments it supports. This heat treatment is achieved by placing the coils in ovens, under vacuum, and applying three stages to them thermal: 50 min at 88 ° C (for vacuum drying); 40 min at 178 ° C; then 10 a.m. 280 ° C.

Table 4 indicates the properties of monofilaments in the post-polycondensed state A-4, B-4, C-4, D-4 thus obtained, respectively from the raw spinning monofilaments A-2, B-2, C-2, D-2.

It can be seen that the raw spinning monofilaments according to the invention (A-2 and B-2) are those which, after heat treatment, lead to the products (A-4 and B-4) presenting the highest toughness (Te> 100 cN / tex) and highest elongation at break (Ar > 2.5%).

Compared to the monofilaments according to the invention, the monofilaments C-4 and D-4 prepared according to the prior art have a significantly lower toughness, an elongation at break weaker, and a general aspect which is degraded: they contain in particular a number important of "kink-bands" at the crossing points of the turns, on the processing coil.

Trial 5

In the following test, using polyester Vectra A900 used for test 1, a oblong monofilament with a title of 230 tex. Its thickness D (smallest dimension of its cross section) is equal to 160 µm, while its width (largest dimension of its cross section) is equal to 1.2 mm; the shape of this monofilament. very flattened, is therefore almost that of a film.

• le capillaire de la filière est de section rectangulaire (avec coins arrondis, pour une meilleure stabilité d'écoulement), de dimensions 5,45 mm par 0,20 mm (soit d = 200 µm ; avec : l/d = 2,5 ; α = 8°);
• pour la fusion du polymère, les trois zones de chauffage successives précédant la pompe de filage sont respectivement à 295°C, 335°C et 330°C (Tx=330°C), la pompe de filage qui suit étant maintenue à la température de 310°C;
• la température de filière (Tf) est égale à 269°C;
• le FEF est égal à 7,6 (Vf égale à 180 m/min);
• la hauteur de la couche d'air, en sortie de filière, est de 150 mm, ce qui correspond à un temps de structuration ts de 0.05 seconde.

We proceed as indicated for test 1 above with the following differences:

• the capillary of the die is of rectangular section (with rounded corners, for better flow stability), of dimensions 5.45 mm by 0.20 mm (i.e. d = 200 μm; with: l / d = 2.5 ; α = 8 °);
• for the polymer melting, the three successive heating zones preceding the spinning pump are respectively at 295 ° C, 335 ° C and 330 ° C (Tx = 330 ° C), the following spinning pump being kept at the temperature 310 ° C;
• the die temperature (Tf) is equal to 269 ° C;
• the FEF is equal to 7.6 (Vf equal to 180 m / min);
• the height of the air layer at the outlet of the die is 150 mm, which corresponds to a structuring time ts of 0.05 seconds.

We note in particular that the above-mentioned relation (2) is verified, ts being well between 1.5.10 ^-6 D ² (i.e. 0.038 s in the present case) and 6.10 ^-6 D ² (i.e. 0.154 s in the present case) :

The properties of the raw oblong spinning monofilament thus obtained are as follows: Te = 57; ΔL = +0.73; Mi = 3050; Ar = 2.6.

The following preferential relationships are therefore verified: 100 ≤ D ≤ 200; ΔL ≥ 0.2; Ar ≥ 2.5; 3000 ≤ Mi <4000.

This monofilament is then subjected to a post-polycondensation heat treatment, in placing the monofilament spool in an oven, under vacuum, and applying the rails and following thermal steps: thermal ramp of 2 ° C / min from room temperature to 195 ° C : then thermal ramp of 0.3 ° C / min from 195 ° C to 241 ° C; then 2 hours at 241 ° C; then crawl thermal from 0.1 ° C / min from 241 ° C to 285 ° C; finally 3 hours at 285 ° C.

The oblong monofilament thus obtained in the post-polycondensed state has, for a titer of 227 tex, a toughness greater than 100 cN / tex (precisely 101 cN / tex, which corresponds to a breaking force about 23 daN), an initial Mi module between 3000 and 4000 cN / tex (precisely 3600 cN / tex) and an elongation at break Ar greater than 3% (precisely 3.4%). It should be noted that the relatively moderate tenacity of the monofilament thus obtained is explained here by a duration of heat treatment which is relatively short; a treatment longer thermal, such as that described for example in test 4 above, leads normally, on this type of polymer, at markedly higher toughness, for example of in the range of 130 to 160 cN / tex.

Reinforcement of rubber articles

The monofilaments according to the invention, in the form of unitary threads (in particular when these are oblong monofilaments or films) or in the form of cables or assemblies, are used preferably for the reinforcement of rubber articles, in particular plies of rubber intended for the manufacture of tires.

For the manufacture of cables or assemblies, methods and devices are used twisting or wiring known to those skilled in the art, which are not described here for the simplicity of the presentation. One can use in particular a technique as described in the WO92 / 12018 application cited above for obtaining cables with layer (s).

These individual cables or wires must be previously glued with one or more adhesive compositions capable of ensuring their adhesion to the rubber matrix that they are intended to strengthen.

• les assemblages ou les monofilaments unitaires passent dans un premier bain de résine époxy puis ils subissent un traitement thermique entre 210 et 260°C pendant un temps compris entre 20 et 120 secondes, par exemple à 250°C pendant 30 secondes ;
• on les fait passer ensuite dans un deuxième bain de colle dite "RFL", à base de latex (par exemple terpolymère butadiène-styrène-vinylpyridine), de résorcine et de formaldéhyde, puis ils subissent un traitement thermique entre 210 et 260°C pendant un temps compris entre 20 et 120 secondes, par exemple à 250°C pendant 30 secondes.

For example, a two-step gluing process is used, as indicated below:

• the assemblies or the unitary monofilaments pass through a first bath of epoxy resin then they undergo a heat treatment between 210 and 260 ° C for a time between 20 and 120 seconds, for example at 250 ° C for 30 seconds;
• they are then passed through a second adhesive bath known as "RFL", based on latex (for example butadiene-styrene-vinylpyridine terpolymer), resorcinol and formaldehyde, then they undergo a heat treatment between 210 and 260 ° C for a time between 20 and 120 seconds, for example at 250 ° C for 30 seconds.

Before gluing, the assemblies or monofilaments can undergo a preliminary treatment activation such as plasma therapy, for example, as described in the application WO92 / 12018 cited above or in application WO92 / 12285, for aramid monofilaments.

The assemblies or monofilaments thus glued and treated are then incorporated in a manner known, by calendering, in the plies of rubber for tires, these plies being intended in particular for crown reinforcement or carcass reinforcement of tires radial.

Advantageously, the monofilaments according to the invention can be used under an oblong shape, therefore not requiring wiring operations, to reinforce the carcass or the top of these radial tires, instead of conventional cables formed of several monofilaments twisted together. With equivalent sheet resistance, the very low thickness D of the oblong monofilaments, compared to the cables, makes it possible to reduce in fact notably the thickness of the rubber plies which they reinforce, and therefore the manufacturing costs; a small thickness D is also favorable for endurance in bending-compression monofilaments, and therefore the endurance of the rubber plies themselves in the tires.

In summary, compared to the raw spinning monofilaments of the prior art, the monofilaments rough spinning of the invention have a new and essential characteristic which is that not to contract hot.

This property gives them many advantages. During the postpolycondensation stage on a support coil, many disadvantages are eliminated such as the risks damage under excessive tension, interfilament bonding, or even appearance "kink-bands"; rewinding operations are no longer necessary. After post-polycondensation treatment, the quality of the treated products is significantly improved; it is therefore no longer necessary in particular to unwind at low voltage or at low speed of the treated monofilaments, which reduces industrial costs so consistent.

The raw spinning monofilaments of the invention, such as those in the post-polycondensed state which derived therefrom, have the advantage over those of the prior art of having, for a given polymer (given stiffness and anisotropy), a lower modulus which is most often combined with higher elongation at break; it has been found that such combination gives monofilaments, for a determined diameter D, resistance in flexion-compression which is improved.

On the other hand, an advantageous characteristic of the spinning method of the invention is that it allows the rate of thermal expansion of monofilaments to be adjusted practically on demand rough spinning, or even their initial modulus and their elongation at break, depending on the intended industrial application; such an adjustment is obtained by controlling the duration of structuring ts of the polymer flow before the liquid quenching, this duration of structuring ts being a direct function of the diameter D of the targeted monofilament.

The raw spinning monofilaments of the invention, like those in the post-polycondensed state which are derived therefrom, can be used in the form of continuous monofilaments or of short fibers: they can optionally be combined with other fibers, threads or monofilaments , for example steel wires, to constitute for example hybrid reinforcing elements. N ^c test ts .DELTA.L You Mid Ar A-1 0020 + 0.55 68 2890 2.5 B-1 0,056 + 0.50 69 3000 2.5 C-1 0,076 + 0.45 70 3270 2.3 D-1 0.112 + 0.40 67 3230 2.3 E-1 0.163 + 0.20 70 3910 2.0 F-1 0.397 - 0.10 74 4340 1.9 Test No. ts .DELTA.L You Mid Ar A-2 0,056 + 0.15 66 2400 2.7 B-2 0081 + 0.07 62 2510 2.6 C-2 0.224 - 0.19 63 3260 2.1 D-2 0407 - 0.25 65 3360 2.0 Test No. D to .DELTA.L You Mid Ar A-3 95 0.05 - 0.30 58 3970 1.6 B-3 105 0.07 - 0.25 58 3790 1.8 C-3 122 0.09 - 0.25 62 3930 1.8 D-3 145 0.13 - 0.18 62 3650 1.9 E-3 168 0.17 + 0.10 59 2690 2.2 F-3 203 0.25 + 0.20 58 2470 2.4 G-3 320 0.61 + 0.30 50 1720 2.8 Test No. Mid Ar You A-4 2640 2.8 115 B-4 2710 2.9 126 C-4 3360 1.7 70 D-4 3380 1.7 68

Claims (22)

1. An as-spun monofilament of thermotropic aromatic polyester(amide), characterised in that it satisfies the following conditions: D ≥ 40; Te > 45; ΔL ≥ 0, D being its diameter or thickness (in µm), Te its tenacity (in cN/tex) and ΔL its variation in length (in %) after 2 minutes at 235 ± 5°C at an initial tension of 0.2 cN/tex.
2. A monofilament according to Claim 1, which satisfies the condition 80 ≤ D ≤ 230.
3. A monofilament according to Claim 2, which satisfies the condition 100 ≤ D ≤ 200.
4. A monofilament according to any one of Claims 1 to 3, which satisfies the conditions: Mi < 4000; Ar > 2, Mi being its initial modulus (in cN/tex) and Ar its elongation at break (in %).
5. A monofilament according to Claim 4, which satisfies the conditions: ΔL ≥ 0.2; Ar ≥ 2.5.
6. A monofilament according to Claims 4 or 5, which satisfies the condition: 2500 < Mi < 4000.
7. A monofilament according to Claim 6, which satisfies the condition: 3000 ≤ Mi < 4000.
8. A monofilament according to any one of claims 1 to 7, which satisfies the condition: Te > 55, preferably Te > 65.
9. A monofilament according to any one of Claims 1 to 8, characterised in that it is made of thermotropic aromatic polyester consisting essentially of recurrent units (A) of 6-oxy-2-naphthoyl and (B) of 4-oxybenzoyl:

   

   the molar ratio A:B lying within a range from 10:90 to 90:10, preferably 20:80 to 30:70.
10. A monofilament of post-polycondensed thermotropic aromatic polyester derived from an as-spun monofilament in accordance with any one of Claims 1 to 9.
11. A monofilament according to Claim 10, which satisfies the following conditions: Mi < 4000; Ar > 2; Te > 100, Mi being its initial modulus (in cN/tex), Ar its elongation at break (in %) and Te its tenacity (in cN/tex).
12. A monofilament according to Claim 11, which satisfies the condition: 2500 < Mi < 4000, preferably 3000 ≤ Mi < 4000.
13. A monofilament according to Claims 11 or 12, which satisfies the condition: Ar > 2.5.
14. A process for spinning a thermotropic aromatic polyester(amide) for obtaining a monofilament of diameter or thickness D in accordance with any one of Claims 1 to 9, characterised in that it comprises the following stages:

    a) melting the polymer;

    b) extruding the molten polymer through a spinneret comprising at least one extrusion capillary;

    c) on emerging from the capillary, structuring the flow of the polymer by stretching in a layer of gaseous fluid, preferably air, for a predetermined time ts;

    d) at the end of the time ts, thermally quenching the flow of polymer thus structured by passing it through a quenching liquid so as to solidify it;

    e) after possibly drying it, winding the monofilament thus obtained,

       the time ts (in seconds) being linked to the diameter or thickness D (in µm) of the as-spun monofilament by the following condition: ts < 6 x 10^-6 D².
15. A process according to Claim 14, characterised in that the quenching liquid is water.
16. A process according to Claims 14 or 15, characterised in that the following condition is satisfied: 1.5 x 10-6 D2 < ts < 6 x 10-6 D2.
17. The use of a monofilament according to any one of Claims 1 to 13 for the reinforcement of articles of plastics material and/or rubber.
18. An article of plastics material and/or rubber reinforced by a monofilament according to any one of Claims 1 to 13.
19. An article according to Claim 18, reinforced by a monofilament according to any one of Claims 3 to 13, consisting of a rubber ply intended for the manufacture of a tyre.
20. An article according to Claim 19, consisting of a carcass reinforcement ply of a radial tyre.
21. An article according to Claim 19, consisting of a crown reinforcement ply of a radial tyre.
22. A tyre reinforced with a monofilament according to any one of Claims 3 to 13.