EP0848767B1 - Cellulose fibres with improved elongation at break, and methods for producing same - Google Patents

Abstract

Fiber made of cellulose formate and fiber made of cellulose regenerated from cellulose formate. These fibers exhibit high tenacity and modulus properties, combined with improved values of elongation at break and of energy at break. Their elongation at break, in particular, is greater than 6%.Methods for producing these fibers. The fiber made of cellulose formate is obtained by spinning a liquid crystal solution of cellulose formate according to the so-called dry-jet-wet spinning method, the coagulation stage and the neutral washing stage which follow both being carried out in acetone. The fiber made of cellulose formate in a highly concentrated aqueous sodium hydroxide solution. The spinning and regeneration methods can be employed in line and continuously.Reinforcing assemblies based on such fibers. Articles reinforced by such fibers or assemblies, these reinforced articles being in particular tires.

Description

The invention relates to fibers of cellulose derivatives and fibers of cellulose. regenerated from these derivatives.

In known manner, the term “cellulose derivatives” is understood here to mean the compounds formed, following chemical reactions, by substitution of the hydroxyl groups of the cellulose, these derivatives also being called substitution derivatives. "Cellulose" means regenerated "a cellulose obtained by a regeneration treatment carried out on a cellulose derivative.

The invention relates more particularly to cellulose formate fibers and cellulose fibers regenerated from this formate, as well as methods for obtaining them such fibers.

Fibers made of cellulose formate and fibers of cellulose regenerated from this formate have especially been described in the international patent application WO 85/05115 (PCT / CH85 / 00065), filed by the applicant, or in the patents equivalents EP-B-179 822 and US-A-4 839 113. These documents describe obtaining spinning solutions based on cellulose formate, by reaction of the cellulose with formic acid and phosphoric acid. These solutions are optically anisotropic, that is to say, they have a liquid crystal state. These documents also describe the cellulose formate fibers obtained by spinning these solutions, using the so-called "dry-jet-wet spinning" technique, as well as cellulose obtained after a regeneration treatment of these formate fibers.

Compared to conventional cellulosic fibers such as rayon fibers or viscose, or to other conventional non-cellulosic fibers such as nylon fibers or polyester for example, all spun from optically isotropic liquids, the cellulose fibers of application WO 85/05115 are characterized by a structure much more orderly, due to the liquid-crystal nature of the spinning solutions from which they come. They thus have very high mechanical properties in extension, in particular very high values of tenacity and modulus, but, in counterpart, are characterized by rather low elongation at break values, these values being on average between 3% and 4%, and not exceeding 4.5%.

However, higher elongation at break values may be desirable when such fibers are used in certain technical applications, in particular as reinforcing elements for a tire, in particular particular of a tire carcass reinforcement.

The primary purpose of the invention is to provide cellulose formate fibers as well as regenerated cellulose fibers which, compared to the fibers of the WO application 85/05115, present a significantly improved elongation at break, as well as high energy properties at break.

The second object of the invention is to obtain the above improvements without reducing the tenacity of the fibers, which is a major advantage of the invention.

Another object of the invention is to obtain regenerated cellulose fibers from cellulose formate, the fatigue resistance of which, in particular in tires, is significantly improved compared to that of regenerated cellulose fibers of the WO 85/05115 cited above.

• Ds ≥ 2 ;
• Te > 45 ;
• Mi > 800 ;
• Ar > 6 ;
• Er > 13,5,

The cellulose formate fiber of the invention is characterized by the following relationships:

• Ds ≥ 2;
• Te>45;
• Mi>800;
• Ar>6;
• Er> 13.5,

Ds being the degree of substitution of the cellulose for formate groups (in%), Te being its toughness in cN / tex, Mi being its initial modulus in cN / tex, Ar being its elongation at break in%. Er being its energy at break in J / g.

• 0 < D_S < 2 ;
• T_E > 60 ;
• M_I > 1000;
• A_R > 6 ;
• E_R > 17,5 ,

The cellulose fiber of the invention. regenerated from cellulose formate, is characterized by the following relationships:

• 0 <D _S <2;
• T _E >60;
• M _I >1000;
• A _R >6;
• E _R > 17.5,

D _S being the degree of substitution of the cellulose for formate groups (in%), T _E being its toughness in cN / tex, M _I being its initial modulus in cN / tex, A _R being its elongation at break in%. E _R being its energy at break in J / g.

The cellulose formate fiber and the above regenerated cellulose fiber are both obtained through new and specific processes which constitute other objects of the invention.

The spinning process of the invention, to obtain the cellulose formate fiber from the invention, consisting in spinning an optically anisotropic solution of cellulose formate in a solvent with phosphoric acid base, according to the spinning method called "dry-jet-wet spinning", is characterized in that the fiber coagulation step and the neutral washing step of the coagulated fiber are both made in acetone.

The regeneration process of the invention, to obtain the regenerated cellulose fiber of the invention, consisting in passing a cellulose formate fiber according to the invention through a regenerating medium, washing it and then drying it, is characterized in that the medium regenerating agent is an aqueous sodium hydroxide solution (NaOH), the concentration of sodium hydroxide, denoted Cs, is greater than 16% (% by weight).

• les assemblages de renforcement comportant chacun au moins une fibre conforme à l'invention, par exemple des câbles, des retors, des fibres multifilamentaires tordues sur elles-mêmes, de tels assemblages de renforcement pouvant être par exemple hybrides, c'est-à-dire composites, comportant des éléments de natures différentes, éventuellement non conformes à l'invention ;
• les articles renforcés par au moins une fibre et/ou un assemblage conformes à l'invention, ces articles étant par exemple des articles en caoutchouc ou en matières plastiques, par exemple des nappes, des courroies, des tuyaux, des enveloppes de pneumatiques, en particulier des armatures de carcasse de pneumatique.

The invention further relates to the following products:

• the reinforcement assemblies each comprising at least one fiber according to the invention, for example cables, twists, multifilament fibers twisted on themselves, such reinforcement assemblies being able to be for example hybrid, that is to say say composites, comprising elements of different natures, possibly not in accordance with the invention;
• articles reinforced with at least one fiber and / or an assembly in accordance with the invention, these articles being for example articles of rubber or plastics, for example plies, belts, pipes, tire casings, in particular in particular tire carcass reinforcements.

The invention will be easily understood with the aid of the description and of the examples not which follow.

I. MEASUREMENTS AND TESTS USED I-1. Degree of polymerization

The degree of polymerization is noted DP. The DP of the cellulose is measured so known, this cellulose being in powder form, or previously transformed into powder.

The inherent viscosity (IV) of the cellulose in solution is first determined, according to Swiss standard SNV 195 598 of 1970, but at different concentrations which vary between 0.5 and 0.05 g / dl. The inherent viscosity is defined by the equation: IV = (1 / C e ) x Ln (t 1 / t 0 ) in which C _e represents the concentration of dry cellulose, t ₁ represents the duration of flow of the dilute polymer solution, t ₀ represents the duration of flow of the pure solvent. in an Ubbelhode viscometer, and Ln represents the natural logarithm. The measurements are carried out at 20 ° C.

The intrinsic viscosity [η] is then determined by extrapolation to concentration none of the inherent viscosity IV.

The weight average molecular mass M _w is given by the Mark-Houwink relation: [η] = K x M w α where the constants K and a are respectively:
K = 5.31 x 10 ^-4 ; α = 0.78. these constants corresponding to the solvent system used for determining the inherent viscosity. These values are given by L. Valtasaari in the document Tappi 48, 627 (1965).

The DP is finally calculated according to the formula: DP = (M w ) / 162, 162 being the molecular weight of the elementary motif of cellulose.

When it comes to determining the DP of cellulose from cellulose formate in solution, we must first isolate this formate, then regenerate the cellulose.

We then proceed as follows:
the solution is first coagulated with water in a dispersing device. After filtration and washing with acetone, a powder is obtained which is then dried in a vacuum oven at 40 ° C for at least 30 minutes. After isolating the formate, the cellulose is regenerated by treating this formate at reflux with normal sodium hydroxide. The cellulose obtained is washed with water, dried and the DP is measured as described above.

I-2. Degree of substitution

The degree of substitution of cellulose for cellulose formate is also called degree of formylation.

The degree of substitution determined by the method described here gives the percentage of alcohol functions of the cellulose which are esterified, that is to say transformed into formate groups. This means that a 100% degree of substitution is obtained if the three alcohol functions of the cellulose motif are all esterified, or that a degree of substitution of 30%, for example, is obtained if 0.9 alcohol function out of three, in medium, is esterified.

The degree of substitution is measured differently depending on whether one characterizes cellulose formate (formate in solution, or fibers in formate) or fibers in cellulose regenerated from cellulose formate.

I-2.1. Degree of substitution on cellulose formate:

If the degree of substitution is measured on cellulose formate in solution, this formate is first isolated from the solution as indicated previously in paragraph I-1. If measured on formate fibers, cut beforehand these fibers in pieces 2 to 3 cm long.

200 mg of cellulose formate thus prepared is weighed with precision and introduced into an Erlenmeyer flask. 40 ml of water and 2 ml of normal sodium hydroxide are added (NaOH 1 N). The mixture is heated at 90 ° C. at reflux for 15 minutes under nitrogen. We thus regenerates the cellulose by retransforming the formate groups into groups hydroxyl. After cooling. excess soda is titrated back with a decinormal hydrochloric acid solution (0.1 N HCl), and the result is degree of substitution.

In the present description, the degree of substitution is noted Ds when it is measured on cellulose formate fibers.

I-2.2. Degree of substitution on regenerated cellulose fibers:

About 400 mg of fiber is cut into 2 to 3 cm long pieces, then accurately weighed and placed in a 100 ml Erlenmeyer flask containing 50 ml of water. 1 ml of normal sodium hydroxide (1N NaOH) is added. The whole is mixed with room temperature, for 15 minutes. This completely regenerates the cellulose by transforming into hydroxyl groups the last formate groups which had resisted the regeneration conducted, after their spinning, directly on continuous fibers. The excess soda is titrated with an acid solution decinormal hydrochloric acid (0.1 N HCl), and the degree of substitution.

In the present description, the degree of substitution is noted D _S when it is measured on regenerated cellulose fibers.

I-3. Optical properties of solutions

The isotropy or optical anisotropy of the solutions is determined by placing a drop of solution to study between crossed linear polarizer and analyzer of a microscope polarization optics, then by observing this solution at rest, that is to say in the absence of dynamic stress, at room temperature.

In known manner, an optically anisotropic solution is a solution which depolarizes the light, that is to say which presents, thus placed between polarizer and crossed linear analyzer, light transmission (colored texture). A optically isotropic solution is a solution which, under the same conditions observation, does not have the above depolarization property, the field of microscope remaining black.

I-4. Mechanical properties of fibers

By "fibers" is meant here multifilament fibers (also called "spun"), made up in a known manner of a large number of elementary filaments of low diameter (low titer). All the mechanical properties below are measured on fibers having been subjected to a preliminary conditioning. By "conditioning prior "means the storage of fibers for at least 24 hours, before measurement, in a standard atmosphere according to European standard DIN EN 20139 (temperature 20 ± 2 ° C; humidity ± 65 ± 2%).

For cellulosic fibers, such prior conditioning makes it possible known to stabilize their moisture content (residual water content) at a level of natural balance less than 15% by weight of dry fiber (approximately 11 to 12%, in average).

The titer of the fibers is determined on at least three samples, each corresponding at a length of 50 m, by weighing this length of fiber. The title is given in tex (weight in grams of 1000 m of fiber).

The mechanical properties of the fibers (toughness, initial modulus, elongation and energy at failure) are measured in a known manner using a tensile machine ZWICK GmbH & Co (Germany) type 1435 or type 1445. The fibers, after have received a small preliminary protection twist (helix angle of approximately 6 °), undergo traction over an initial length of 400 mm at a speed of 200 mm / min (or at a speed of 50 mm / min only when their elongation at the failure does not exceed 5%). All results given are an average of 10 measures.

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 approximately 0.11 g / den (gram per denier)). The initial module is defined as the slope of the linear part of the curve Force-Elongation, which occurs just after the standard pretension of 0.5 cN / tex. The elongation at break is indicated as a percentage. The energy at break is given in J / g (joule per gram), that is to say per unit mass of fiber.

II. CONDITIONS FOR CARRYING OUT THE INVENTION

We first describe the production of spinning solutions, then the spinning of these solutions for obtaining fibers in cellulose formate. In a third paragraph is explained the step of regeneration of cellulose formate fibers, to obtaining regenerated cellulose fibers.

II-1. Realization of spinning solutions

Cellulose formate solutions are made by mixing cellulose, formic acid, and phosphoric acid (or an acid-based liquid phosphoric), as indicated for example in the aforementioned application WO 85/05115.

Cellulose can be in various forms, in particular in the form of a powder, prepared for example by spraying a plate of crude cellulose. Of preferably, its initial water content is less than 10% by weight, and its DP included between 500 and 1000.

Formic acid is esterification acid, phosphoric acid (or liquid based on phosphoric acid) being the solvent for cellulose formate, called "solvent" or "spinning solvent" in the description below. -after. In general, the phosphoric acid used is orthophosphoric acid (H ₃ PO ₄ ), but it is possible to use other phosphoric acids, or a mixture of phosphoric acids. The phosphoric acid can, depending on the case, be used solid, in the liquid state, or dissolved in formic acid.

Preferably the water content of these two acids is less than 5% by weight: they can be used alone or possibly contain, in small proportions, other organic and / or mineral acids, such as acetic acid, sulfuric acid or acid hydrochloric for example.

In accordance with the description made in the aforementioned application WO 85/05115, the concentration of cellulose in the solution, noted "C" below, can vary widely measure; C concentrations between 10% and 30% (% by weight of cellulose - calculated on the basis of non-esterified cellulose - on the total weight of the solution) are for example possible, these concentrations being in particular a function of the degree of cellulose polymerization. The weight ratio (formic acid / acid phosphoric) can also be adjusted within a wide range.

When making cellulose formate, the use of formic acid and phosphoric acid makes it possible to obtain both a high degree of substitution in cellulose formate, generally greater than 20%, without excessive reduction in the degree initial polymerization of cellulose, as well as a homogeneous distribution of these formate groups, both in the amorphous zones and in the crystalline zones of the cellulose formate.

Kneading means suitable for obtaining a solution are known from those skilled in the art: they must be able to knead, knead properly, preferably cellulose and acids at an adjustable speed until the solution is obtained. Through "solution" means here, in known manner, a homogeneous liquid composition in which no solid particle is visible to the naked eye. Mixing can be carried out for example in a mixer with Z-shaped arms, or in a screw mixer continuously. These mixing means are preferably equipped with a device vacuum evacuation and a heating and cooling device allowing adjust the temperature of the mixer and its contents, for example to speed up dissolution operations, or to control the temperature of the solution being training.

By way of example, the following procedure can be used:

It is introduced into a mixer with a double envelope, comprising arms in Z and a extrusion screw, cellulose powder (whose humidity is in equilibrium with ambient air humidity). A mixture of orthophosphoric acid is then added (99% crystalline) and formic acid. containing for example three quarters of acid orthophosphoric for a quarter of formic acid (parts by weight). The whole is mixed for a period of about 1 to 2 hours for example the temperature of the mixture being maintained between 10 and 20 ° C, until a solution is obtained.

The spinning solutions thus obtained are ready to spin, they can be transferred directly, for example by means of an extrusion screw placed at the outlet of the mixer, to a spinning machine to be spun there, without further processing than usual operations such as degassing or filtration for example.

• leur concentration en cellulose est comprise entre 15 % et 25 % (% en poids), calculée sur la base d'une cellulose non estérifiée ;
• leur concentration en acide formique total (c'est-à-dire la part d'acide formique consommée pour l'estérification plus la part d'acide formique libre restant dans la solution finale) est comprise entre 10 % et 25 % (% en poids) ;
• leur concentration en acide phosphorique (ou en liquide à base d'acide phosphorique) est comprise entre 50 % et 75 % (% en poids) ;
• le degré de substitution de la cellulose en groupes formiate, dans la solution, est compris entre 25 % et 50 %, de manière plus préférentielle compris entre 30 % et 45 % ;
• le degré de polymérisation de la cellulose, en solution, est compris entre 350 et 600;
• elles contiennent moins de 10 % d'eau (% en poids).

The spinning solutions used for implementing the invention are optically anisotropic solutions. Preferably, these spinning solutions have at least one of the following characteristics:

• their cellulose concentration is between 15% and 25% (% by weight), calculated on the basis of a non-esterified cellulose;
• their concentration of total formic acid (that is to say the part of formic acid consumed for the esterification plus the part of free formic acid remaining in the final solution) is between 10% and 25% (% in weight);
• their concentration in phosphoric acid (or in liquid based on phosphoric acid) is between 50% and 75% (% by weight);
• the degree of substitution of the cellulose for formate groups in the solution is between 25% and 50%, more preferably between 30% and 45%;
• the degree of polymerization of the cellulose, in solution, is between 350 and 600;
• they contain less than 10% water (% by weight).

II-2. Spinning solutions

The spinning solutions are spun according to the so-called "dry-jet-wet-spinning" technique: this technique uses a non-coagulating fluid layer, generally air, placed in outlet of the die, between the die and the coagulation means.

At the outlet of the mixing and dissolution means. the spinning solution is transferred to the spinning block where it supplies a spinning pump. From this pump spinning, the solution is extruded through at least one die, preceded by a filter. It is during the journey to the sector that the solution is gradually brought to the desired spinning temperature, generally between 35 ° C and 90 ° C, depending on the nature of the solutions, preferably between 40 ° C and 70 ° C. So we mean by "spinning temperature" means the temperature of the spinning solution at the time of its extrusion through the die.

Each die can include a variable number of extrusion capillaries, which number can vary for example from 50 to 1000. The capillaries are generally of cylindrical shape, their diameter possibly varying for example from 50 to 80 µm (micrometers).

At the outlet of the die, we therefore obtain a liquid extrudate made up of a variable number of elementary liquid veins. Each elementary liquid vein is stretched (see below spinning factor) in a non-coagulating fluid layer, before enter the coagulation zone. This non-coagulating fluid layer is in generally a layer of gas, preferably air, the thickness of which can vary from a few mm to several tens of mm (millimeters), for example from 5 mm to 100 mm, depending on the specific spinning conditions; in known manner, by thickness of the non-coagulating layer the distance between the underside of the channel, arranged horizontally, and the entrance to the coagulation zone (surface of the coagulating liquid).

After crossing the non-coagulating layer, all the liquid veins thus stretched enter the coagulation zone and come into contact with the coagulating medium. Under the action of the latter, they are transformed, by precipitation of the cellulose formate and extracting the spinning solvent, into solid cellulose formate filaments which thus form a fiber.

The coagulating medium used is acetone.

The temperature of the coagulating medium. noted Tc, is not a critical parameter for the implementation of the invention. For example, for spinning solutions containing 22% by weight of cellulose, it was observed that a variation in temperature Tc, in the entire temperature range from -30 ° C to 0 ° C, had practically no of incidence on the mechanical properties of the fibers obtained.

Preferably a negative temperature Tc, that is to say less than 0 ° C, will be chosen, and even more preferably less than -10 ° C.

Those skilled in the art will be able to adjust the temperature of the coagulating medium as a function of the characteristics of the spun solution, and of the targeted mechanical properties, by tests simple optimization. In general, the temperature Tc will be chosen as much lower than the concentration C of the spinning solution will be lower.

The level of spinning solvent in the coagulating medium is preferably stabilized at a level below 15%, even more preferably below 10% (% in weight of coagulating medium).

The coagulation means to be used are known devices, composed by example of baths, pipes and / or cabins, containing the coagulating medium and in which the fiber circulates during formation. A coagulation bath is preferably used arranged under the die, at the outlet of the non-coagulating layer. This bath is generally extended at its base by a vertical cylindrical tube, called "spinning tube", in which passes the coagulated fiber and circulates the coagulating medium.

The depth of the coagulating medium in the coagulation bath, measured from the inlet of the bath up to the entry of the spinning tube, can vary from a few millimeters to a few centimeters for example, according to the specific conditions of realization of the invention, in particular according to the spinning speeds used. The coagulation bath can be extended if necessary by additional coagulation devices, by example by other baths or cabins, placed at the outlet of the spinning tube, by example after a horizontal reference point.

a) le taux de solvant résiduel dans la fibre, à la sortie des moyens de coagulation (noté Rs), est inférieur à 100 % en poids de fibre en formiate sèche ;

b) la contrainte de tension subie par la fibre, à la sortie des moyens de coagulation (notée σ_c), est inférieure à 5 cN/tex, et, de manière encore plus préférentielle, de manière à ce que les deux caractéristiques a) et b) ci-dessus soient simultanément vérifiées.

Preferably, the method of the invention is implemented so that at least one of the following characteristics is verified:

a) the level of residual solvent in the fiber, at the outlet of the coagulation means (denoted Rs), is less than 100% by weight of fiber in dry formate;

b) the stress of tension undergone by the fiber, at the exit of the coagulation means (noted σ _c ), is lower than 5 cN / tex, and, even more preferably, so that the two characteristics a) and b) above are simultaneously verified.

Thus, according to the above preferential conditions, the fiber is left in contact with the coagulating medium until a substantial part of the spinning solvent is extracted from the fiber. On the other hand, during this coagulation phase, we try to maintain the tensions undergone by the fiber at a moderate level: to control this, we will measure these voltages immediately at the output of the coagulation means, using tensiometers appropriate.

In general, if it is desired above all to favor the elongation properties at break of the formate fibers. the invention will preferably be implemented so that the following two relationships are verified:
Rs <50%; σ _c <2 cN / tex.

For measuring the residual solvent Rs present in the formate fiber coagulated, we proceed for example as follows: fiber is taken at the exit from the coagulation means, with its coagulating medium; then she is wiped in surface with absorbent paper, without pressure, so as to eliminate most of the coagulating medium (acetone) which is contained in the surface layer surrounding the fiber, and which itself contains a certain fraction of spinning solvent (acid phosphoric or liquid based on phosphoric acid) already extracted from the fiber; we wash then completely the fiber with water, in a laboratory device, so as to completely extract the phosphoric acid which it contains, then titrate in return this phosphoric acid with soda; for more precision, the measurement is repeated 5 times and the average is calculated.

At the outlet of the coagulation means, the fiber is taken up on a device drive, for example on motorized cylinders. The speed of the spun product, on this drive device, is called "spinning speed" (or call speed or training): this is the speed of travel of the fiber through the installation of spinning, once the fiber is formed. The relationship between spinning speed and speed of extrusion of the solution through the die, defines what is called, so known, the spinning stretch factor (abbreviated as FEF), which is for example included between 2 and 10.

Once coagulated, the fiber must be washed until neutral. By "neutral washing", we means any washing operation allowing all or almost all of the fiber to be extracted spinning solvent.

Those skilled in the art have naturally been inclined up to now to use water as a medium. washing: in a well known manner, water is indeed the "natural" swelling medium of fibers of cellulose or cellulose derivatives (see for example US-A-4,501,886), and therefore the medium likely to offer, a priori, the best washing efficiency.

For example, patents or patent applications EP-B-220642, US-A-4,926,920, WO 94/17136, as in the aforementioned application WO 85/05115 (page 72, examples II-1 and below), describe the use of water, at the outlet of the coagulation means, for the washing of cellulose formate fibers.

However, such a conventional step of washing with water does not make it possible to obtain cellulose formate fibers according to the invention.

Quite surprisingly, the Applicant has found that the acetone used as a washing medium, despite a washing power which is, in known manner, significantly weaker than that of water, leads to fibers which, once completed (i.e. washed until neutral, then dried), properties very clearly improved, firstly with regard to their elongation at break, when compared to the fibers described in application WO 85/05115.

For the implementation of the process of the invention, the step of coagulating the fiber and the neutral washing step of the coagulated fiber must both be carried out in acetone.

The temperature of the washing acetone is not a critical parameter of the process. he goes However, it is obvious that too low temperatures will be avoided in order to favor the washing kinetics. Preferably, the temperature of the washing acetone, denoted T1, will be chosen positive (by this is meant a temperature equal to or greater than 0 ° C), and even more preferably greater than + 10 ° C. Advantageously, uncooled acetone can be used, i.e. acetone at temperature ambient, the washing operation then preferably being carried out in an atmosphere controlled.

Known washing means can be used, for example consisting of baths containing the washing acetone and in which the fiber to be washed circulates. The times of washing in acetone can vary, typically, from a few seconds to a few tens of seconds, depending on the specific conditions of implementation of the invention.

Of course, the washing medium as well as the coagulating medium may contain all two of the constituents other than acetone, without the spirit of the invention being modified, provided that these other constituents are present only in minor proportion; the total proportion of these other constituents will preferably be less than 15%, more preferably less than 10% (% by total weight of coagulating medium or washing medium). More particularly, if water is present in the acetone of coagulation or washing, its content will preferably be less than 5%.

After washing, the cellulose formate fiber is dried by any suitable means, in order to remove the washing acetone. Preferably, the level of acetone leaving the drying means is adjusted to a rate less than 1% by weight of dry fiber. For the drying operation, one can operate for example by continuously scrolling the fiber on heating rollers, or use, as a main or complementary, a previously heated nitrogen blowing technique. Of preferably, a drying temperature at least equal to 60 ° C. is used, more preferably between 60 ° C and 90 ° C.

The method of the invention can be implemented in a very wide range of speeds of wiring, which can vary from several tens to several hundred meters at the minute, for example at 400 m / min or 500 m / min or more. Advantageously, the spinning speed is at least equal to 100 m / min, more preferably at least equal to 200 m / min.

If we want to isolate the fiber in cellulose formate, that is to say not to regenerate it all immediately, in particular to check its mechanical properties before the operations of regeneration, the washing step will preferably be carried out so that the rate residual spinning solvent in the finished fiber, i.e. washed and dried, does not exceed 0.1% to 0.2% by weight, relative to the weight of dry fiber.

The cellulose formate fiber thus spun can also be sent directly to the means of regeneration, online and continuously, in order to prepare a fiber in regenerated cellulose.

II-3. Regeneration of formate fibers

In a known manner, a process for regenerating a fiber into a cellulose derivative consists in treating this fiber in a regenerating medium so as to eliminate the almost all of the substituent groups (so-called saponification treatment), to wash the fiber thus regenerated and then dried, these three operations being in principle carried out in continuous on the same treatment line called "regeneration line".

Regarding cellulose formate, the regenerating medium usually used is a weakly concentrated aqueous sodium hydroxide solution (sodium hydroxide NaOH), do not containing only a few% soda (% by weight), for example from 1 to 3% (see par example PCT / AU91 / 00151).

Low concentrated aqueous sodium hydroxide solutions not exceeding 5% (% by weight), have also been described in patents or Patent applications EP-B-220642, US-A-4,926,920, WO 94/17136 and WO 95/20629 for the regeneration of cellulose formate fibers. They were used by the Applicant for the regeneration of cellulose formate fibers described in the WO 85/05115 cited above, as for the regeneration of formate fibers cellulose of the present invention; these weakly concentrated solutions turn out to be quite satisfactory for conducting the regeneration proper, that is to say for eliminating almost all of the substituent formate groups: they make it possible to obtain without difficulty regenerated fibers whose degree of substitution in formate groups is less than 2%.

In an attempt to increase the sodium hydroxide concentrations above 5%, the applicant has found that the filaments of the cellulose formate fibers (whether these are conforming or not to the invention) underwent partial, superficial dissolution, as soon as that the sodium hydroxide concentration reached and exceeded approximately 6% by weight, the medium regenerating then becoming a true solvent for cellulose formate. Such a dissolution, even partial, is completely detrimental to the mechanical properties of the fiber: presence of bonded filaments, drop in resistance of the attacked filaments, fiber washing difficulties, etc.

Such problems of parasitic dissolution were moreover foreseeable, knowing by example that viscose type cellulosic fibers are partially or totally soluble in 10% soda (see P.H. Hermans, "Physics and Chemistry of Cellulose Fibers ", 1st part, Elsevier 1949), or that 5% of native cellulose dissolve in an 8 to 10% aqueous solution of NaOH (see T. Yamashiki, Journal of Applied Polymer Science, vol. 44, 691-698, 1992).

Given the various elements above, the skilled person was therefore all naturally inclined to use aqueous solutions of weakly concentrated soda, for the regeneration of cellulose formate fibers.

However, by continuing to increase the sodium hydroxide concentration of the regenerating medium well beyond the above 5 to 6%, the plaintiff has found, quite surprisingly, that beyond a certain concentration threshold, not only parasitic dissolution phenomena disappeared, but still and above all that certain properties of the regenerated fiber were improved very significantly, notably the elongation at break and the energy at break.

In other words, if a conventional regenerating medium (i.e. weakly concentrated in soda) is certainly quite sufficient to regenerate cellulose formate fibers, such a medium does not however make it possible to obtain the regenerated cellulose fibers according to the invention.

The process of the invention, for obtaining a regenerated cellulose fiber in accordance with the invention, by regeneration of a cellulose formate fiber, is characterized in that that the regenerating medium is a highly concentrated aqueous sodium hydroxide solution, of which the sodium hydroxide concentration, denoted Cs, is greater than 16% (% by weight).

Preferably, a Cs concentration greater than 18% is used, and still more preferred, a concentration of between 22% and 40%; we have indeed found that such concentration ranges were, as a rule, more particularly beneficial to the elongation of the regenerated fiber, the area with an optimal concentration of between 22% and 30%.

For the implementation of the regeneration process of the invention, one starts from preferably a cellulose formate fiber according to the invention, having in particular an elongation at break Ar greater than 6%.

The regeneration line consists concretely, and in a classic way, of regeneration means, followed by washing means, themselves followed by means of drying. All these devices are not critical for the implementation of the invention, and those skilled in the art will be able to define them without difficulty. The means of regeneration and washing may consist in particular of baths, pipes, tanks, cabins, in which circulate the regenerating medium or the washing medium. Cabins, for example, each with two cylinders can be used motorized around which the fiber to be treated is wound, this fiber then being showered with the liquid medium used (regenerating or washing).

The residence times in the regeneration means will of course have to be adjusted so as to regenerate the formate fibers substantially, and thus to verify the following relationship on the final regenerated fiber:
0 <D _S <2.

Those skilled in the art will be able to adjust these residence times, which, depending on the conditions particular implementation of the invention, may vary for example from 1 to 2 seconds up to 1 to 2 tens of seconds.

The washing medium is preferably water. Indeed, after the operation of above regeneration, the cellulose fiber can be washed with its swelling medium natural. that is to say with water, the latter having the best washing. Water is used at room temperature, or at a higher temperature, if necessary, to increase the washing kinetics. At this wash water can be possibly added a neutralizing agent for the soda not consumed, by example of formic acid.

The drying means may consist, for example, of heated tunnels ventilated through which the washed fiber circulates, or in heating cylinders on which the fiber is wound. The drying temperature is not critical, and may vary over a wide range, in particular from 80 ° C to 240 ° C or more, depending on the specific conditions for implementing the invention, in particular according to the speeds of passage on the regeneration line. Preferably a temperature not exceeding 200 ° C.

At the outlet of the drying means, the fiber is taken from a take-up reel, and controls its residual humidity level. Preferably, the conditions of drying (temperature and time) will be adjusted so that the humidity residual is between 10% and 15%, even more preferably in the range of 12% to 13% by weight of dry fiber.

Typically. washing and drying times required vary by a few seconds to a few tens of seconds, depending on the means used and the conditions particular embodiments of the invention.

During the passage through the regeneration line. we will of course avoid tensions excessive in order not to damage the fiber on the one hand, not to lose on the other hand a significant part of the potential elongation at break offered by the use of the medium regenerating concentrated in soda. These tensions are generally difficult to access within the various means employed: they can be checked and measured at the input of these different means, using suitable tensiometers.

This is how if we wish to favor the elongation at break of the fiber regenerated, the voltage constraints at the input of the regeneration means, washing means and drying means, will preferably be chosen lower at 10 cN / tex. and even more preferably less than 5 cN / tex.

In real industrial conditions of regeneration, and in particular for high regeneration speeds. the lower limits of these voltage constraints are are generally in the region of 0.1 to 0.5 cN / tex, lower values being not realistic from an industrial point of view. and even undesirable. We noticed in particular that the mechanical properties of regenerated fibers could be adjusted more or less by playing on these tension constraints.

The regeneration speed (denoted Vr), that is to say the speed of passage of the fiber to across the regeneration line, can vary from several tens to several hundred meters per minute, for example up to 400 or 500 m / min or more; so advantageous, this speed Vr is at least equal to 100 m / min, more preferably at least equal to 200 m / min.

Finally, the regeneration method of the invention is preferably implemented in line and continuously with the spinning method of the invention, so that the entire production chain. from the extrusion of the solution through the die to drying of the regenerated fiber, or uninterrupted.

III. EXAMPLES OF EMBODIMENT OF THE INVENTION

The tests described below can either be tests in accordance with the invention, or tests not in accordance with the invention.

III-1. CELLULOSE FORMAT FIBERS A) Fibers in accordance with the invention (Table 1):

A total of 14 spinning tests of cellulose formate fibers are carried out, according to the spinning method of the invention, and in particular conforming to the indications provided in paragraphs II-1 and II-2 above.

The coagulation step and the neutral washing step of the coagulated fiber are all two carried out in acetone.

Table 1 gives both the specific conditions for carrying out the process of the invention, and the properties of the fibers obtained.

N° Essai : numéro de l'essai (référencé de A-1 à A-14);

N : nombre de filaments de la fibre;

C : concentration en cellulose dans la solution de filage (% en poids);

DP : degré de polymérisation de la cellulose dans la solution de filage;

Vf : vitesse de filage (en m/min);

Tc : température du milieu coagulant (en °C);

Rs : taux de solvant résiduel dans la fibre à la sortie des moyens de coagulation (% en poids);

σ_c : contrainte de tension subie par la fibre à la sortie des moyens de coagulation (en cN/tex);

Ti : titre de la fibre (en tex);

Te : ténacité de la fibre (en cN/tex);

Mi : module initial de la fibre (en cN/tex);

Ar : allongement à la rupture de la fibre (en %);

Er : énergie à la rupture de la fibre (en J/g);

Ds : degré de substitution de la cellulose en groupes formiate, dans la fibre (en %);

The abbreviations and the units used in this table 1 are as follows:

Test No .: test number (referenced from A-1 to A-14);

N: number of filaments of the fiber;

C: cellulose concentration in the spinning solution (% by weight);

DP: degree of polymerization of the cellulose in the spinning solution;

Vf: spinning speed (in m / min);

Tc: temperature of the coagulating medium (in ° C);

Rs: rate of residual solvent in the fiber at the outlet of the coagulation means (% by weight);

σ _c : tension stress undergone by the fiber at the exit of the coagulation means (in cN / tex);

Ti: fiber title (in tex);

Te: fiber tenacity (in cN / tex);

Mi: initial fiber modulus (in cN / tex);

Ar: elongation at break of the fiber (in%);

Er: energy at break of the fiber (in J / g);

Ds: degree of substitution of cellulose for formate groups in the fiber (in%);

• toutes les solutions de filage sont préparées à partir de cellulose en poudre (de teneur initiale en eau égale à environ 8 % en poids, de degré de polymérisation compris entre 500 et 600), d'acide formique et d'acide orthophosphorique (contenant chacun environ 2.5 % en poids d'eau) ;
• ces solutions contiennent (% en poids) de 16 à 22 % de cellulose, de 60 à 65 % d'acide phosphorique, et de 18 à 19 % d'acide formique (total), le rapport pondéral (acide formique/acide phosphorique) initial étant égal à 0,30 environ ;
• ces solutions sont optiquement anisotropes, et contiennent au total moins de 10 % d'eau (% en poids);
• le degré de substitution de la cellulose, dans les solutions, est compris entre 40 et 45 % pour les solutions contenant 16 % en poids de cellulose, entre 30 et 40 % pour les autres solutions plus concentrées ;
• les filières comportent 500 ou 1000 capillaires de forme cylindrique, de diamètre 50 ou 65 µm ;
• les températures de filage sont comprises entre 40 et 50°C;
• les valeurs de FEF sont comprises entre 2 et 6 (entre 2 et 4 pour les essais A-1, A-5 à A-9, A-14 ; entre 4 et 6 pour les autres essais);
• la couche fluide non coagulante est constituée par une couche d'air (épaisseur variant de 10 à 40 mm selon les essais) ;
• le taux d'acide phosphorique. dans le milieu coagulant, est stabilisé à un niveau inférieur à 10 % (% en poids de milieu coagulant) ;
• la température de l'acétone de lavage (Tl) est toujours positive, comprise entre 15 et 20°C :
• le séchage de la fibre est réalisé à 70°C, par passage sur des cylindres chauffants, avec en complément un soufflage d'azote chauffé à 80°C; le taux d'acétone en sortie des moyens de séchage est inférieur à 0,5 % (% en poids de fibre sèche) ;
• sur la fibre terminée, i.e. lavée et séchée. le taux d'acide phosphorique résiduel est inférieur à 0,1 % (% en poids de fibre sèche).
  

In addition, the following special conditions are used to carry out these tests:

• all spinning solutions are prepared from powdered cellulose (initial water content equal to about 8% by weight, degree of polymerization between 500 and 600), formic acid and orthophosphoric acid (each containing about 2.5% by weight of water);
• these solutions contain (% by weight) from 16 to 22% of cellulose, from 60 to 65% of phosphoric acid, and from 18 to 19% of formic acid (total), the weight ratio (formic acid / phosphoric acid) initial being equal to approximately 0.30;
• these solutions are optically anisotropic, and contain in total less than 10% water (% by weight);
• the degree of substitution of the cellulose in the solutions is between 40 and 45% for the solutions containing 16% by weight of cellulose, between 30 and 40% for the other more concentrated solutions;
• the channels include 500 or 1000 capillaries of cylindrical shape, with a diameter of 50 or 65 μm;
• the spinning temperatures are between 40 and 50 ° C;
• the values of FEF are between 2 and 6 (between 2 and 4 for tests A-1, A-5 to A-9, A-14; between 4 and 6 for other tests);
• the non-coagulating fluid layer consists of an air layer (thickness varying from 10 to 40 mm depending on the tests);
• the phosphoric acid level. in the coagulating medium, is stabilized at a level of less than 10% (% by weight of coagulating medium);
• the temperature of the washing acetone (Tl) is always positive, between 15 and 20 ° C:
• the drying of the fiber is carried out at 70 ° C, by passing over heating cylinders, with in addition a blowing of nitrogen heated to 80 ° C; the acetone level at the outlet of the drying means is less than 0.5% (% by weight of dry fiber);
• on the finished fiber, ie washed and dried. the level of residual phosphoric acid is less than 0.1% (% by weight of dry fiber).
  

On reading Table 1, it is noted in particular that with the exception of test A-13, the temperature Tc of the coagulation acetone is always negative, less than - 10 ° C in the majority of cases.

The DP of the cellulose in the solution is between 400 and 450, which shows in particular a weak depolymerization after dissolution.

It is further noted that for all the tests in Table 1, at least one of the following preferential conditions is satisfied:
Rs <100%; σ _c <5 cN / tex,
and that these two relationships are simultaneously verified in the majority of cases.

Even more preferably, the following two relationships are verified simultaneously:
Rs <50%; σ _c <2 cN / tex.

On the other hand. spinning speeds are high, since they are equal for the most at 150 m / min.

All the mechanical properties indicated in table 1 are values averages calculated over 10 measurements, except for the title (average over 3 measurements), the standard deviation on the mean (in% of this mean) being generally between 1 and 2.5%.

• Ds ≥ 2 ;
• Te > 45 ;
• Mi > 800 ;
• Ar > 6 ;
• Er > 13,5 .

On reading Table 1, it can be seen that all of the fibers verify the following relationships:

• Ds ≥ 2;
• Te>45;
• Mi>800;
• Ar>6;
• Er> 13.5.

Preferably, for the cellulose formate fibers of the invention, the values of Ds are between 25 and 50%. We see that in these examples, they are all between 30 and 45%: in practice, they are identical to substitution degree values measured on spinning solutions corresponding.

Preferably, their elongation at break Ar is greater than 7% (examples A-4 to A-6), even more preferably greater than 8% (examples A-5 and A-6).

In addition, these fibers in Table 1 mostly verify the following preferential relationships:
Te>60;Mi>1200;Er> 20.

Even more preferably, at least one of the following relationships is verified:
Te>70;Mi>1500;Er> 25.

For all the examples in Table 1, we also note that the following relation is verified:
Mid <1800.

However, particularly high initial modulus values, for example between 1800 and 2200 cN / tex, or even more, are still accessible on formate fibers according to the invention, normally to the detriment of elongation at break, adapting the parameters of the spinning process according to the invention. This could be achieved in particular by increasing the constraints of voltages on the spinning line, for example at the output of the coagulation means, during washing or during the drying of the fiber; we observed also that the use of relatively high C concentrations, in particular between 24 and 30%, were in favor of obtaining initial modules and very high toughness.

B) Fibers not in accordance with the invention (Table 2):

5 spinning tests (referenced from B-1 to B-5) of formate fibers are carried out. cellulose, according to a spinning process not in accordance with the invention.

The general and specific conditions used for spinning are the same than those used for the fibers in table 1 above, with one exception: the neutral washing step of the coagulated fiber is carried out with water (as in WO 85/05115 cited above), and not with acetone. This water from washing is industrial water, at a temperature close to 15 ° C. On the other hand the fibers contain 250 to 1000 filaments.

Table 2 gives both the specific conditions for carrying out the process of the invention, and the properties of the fibers obtained. The abbreviations and the units used in this table 2 are the same as for the previous table 1.

It is noted that these fibers of table 2, spun according to the method taught by the WO 85/05115 cited above, may have characteristics quite interesting tenacity and initial modulus; in particular, after a stage of conventional regeneration according to the prior art (aqueous NaOH solution weakly concentrated), they can be transformed into regenerated fibers having very high toughness (110 to 120 cN / tex, or even more) combined with very high initial modulus values (3000 to 3500 cN / tex, or even more).

However, none of these fibers in Table 2 is in accordance with the invention, the following relationship not being verified:
Ar> 6.

III-2. REGENERATED CELLULOSE FIBERS A) Fibers in accordance with the invention (Table 3):

A total of 23 regeneration tests of cellulose formate fibers are carried out, according to the regeneration process of the invention, according to the indications provided in paragraph II-3 above.

All these regeneration tests are conducted online and continuously with the spinning operation, the latter being carried out in accordance with the spinning of the invention: in particular, the coagulation step and the washing step Neutral coagulated fiber are both made in acetone.

The regenerating medium is an aqueous sodium hydroxide solution, the concentration Cs is in any case greater than 16%.

Table 3 gives both specific conditions for carrying out the process of the invention, and the properties of the fibers obtained.

N° Essai : numéro de l'essai (référencé de C-1 à C-23);

N : nombre de filaments de la fibre régénérée;

Cs : concentration en soude du milieu régénérant (% en poids);

Vr : vitesse de régénération (en m/min);

T_I : titre de la fibre (en tex);

T_E : ténacité de la fibre (en cN/tex);

M_I : module initial de la fibre (en cN/tex);

A_R : allongement à la rupture de la fibre (en %);

E_R : énergie à la rupture de la fibre (en J/g);

The abbreviations and the units used in this table 3 are as follows:

Test No .: test number (referenced from C-1 to C-23);

N: number of filaments of the regenerated fiber;

Cs: concentration of sodium hydroxide in the regenerating medium (% by weight);

Vr: regeneration speed (in m / min);

T _I : title of the fiber (in tex);

T _E : tenacity of the fiber (in cN / tex);

M _I : initial modulus of the fiber (in cN / tex);

A _R : elongation at break of the fiber (in%);

E _R : energy at break of the fiber (in J / g);

• les fibres en formiate de cellulose de départ, dont un échantillon (quelques centaines de mètres) a été systématiquement prélevé en sortie des moyens de filage, pour contrôle de leurs propriétés mécaniques, sont toutes conformes à l'invention ; en particulier, elles possèdent toutes un allongement à la rupture supérieur à 6 % ;
• le milieu régénérant utilisé est à température ambiante (environ 20°C);
• les moyens de régénération, de lavage, et de séchage sont constitués par des cabines équipées de cylindres motorisés sur lesquels vient s'enrouler la fibre à traiter ;
• la régénération étant opérée en ligne et en continu avec le filage, la vitesse de régénération Vr indiquée au tableau 3 (de 55 à 200 m/min) est donc égale à la vitesse de filage Vf ;
• le lavage est réalisé avec de l'eau industrielle à une température de 15°C environ ;
• le séchage de la fibre lavée est réalisé sur des cylindres chauffants, à différentes températures variant de 80°C à 240°C, selon le schéma particulier ci-après: de 80°C à 120°C pour les essais C-2, C-3, C-5, C-10, C-17 ; à 240°C pour l'essai C-11 ; de 160°C à 190°C pour les autres essais ;
• les contraintes de tension mesurées à l'entrée des moyens de régénération, de lavage, et de séchage sont toujours inférieures à 10 cN/tex, dans la majorité des cas inférieures à 5 cN/tex, sauf pour les essais C-7, C-9, C-15 où l'on a mesuré une tension égale ou supérieure à 5 cN/tex à l'entrée d'au moins un des moyens ci-dessus ; ces contraintes de tension sont inférieures à 2 cN/tex à chaque entrée des trois moyens énoncés ci-dessus (régénération, lavage et séchage) pour un grand nombre d'essais: C-2 à C-5, C-10 à C-11, C-13 à C-14, C-16 à C-23 ;
• les temps de séjour dans les moyens de régénération sont de l'ordre de 15 s, comme dans les moyens de lavage, alors qu'ils sont de l'ordre de 10 s dans les moyens de séchage ;
• à la sortie des moyens de séchage, les fibres présentent un taux d'humidité résiduelle de l'ordre de 12 % à 13 % (% en poids de fibre sèche).
  

In addition, the following special conditions are used to carry out these tests:

• the starting cellulose formate fibers, a sample of which (a few hundred meters) was systematically taken at the outlet of the spinning means, for checking their mechanical properties, all conform to the invention; in particular, they all have an elongation at break greater than 6%;
• the regenerating medium used is at room temperature (about 20 ° C);
• the regeneration, washing and drying means consist of cabins fitted with motorized cylinders on which the fiber to be treated is wound;
• the regeneration being carried out in line and continuously with the spinning, the regeneration speed Vr indicated in table 3 (from 55 to 200 m / min) is therefore equal to the spinning speed Vf;
• washing is carried out with industrial water at a temperature of about 15 ° C;
• drying of the washed fiber is carried out on heating cylinders, at different temperatures varying from 80 ° C to 240 ° C, according to the specific scheme below: from 80 ° C to 120 ° C for tests C-2, C -3, C-5, C-10, C-17; at 240 ° C for test C-11; from 160 ° C to 190 ° C for the other tests;
• the tension stresses measured at the input of the regeneration, washing and drying means are always less than 10 cN / tex, in the majority of cases less than 5 cN / tex, except for tests C-7, C -9, C-15 where a tension equal to or greater than 5 cN / tex has been measured at the input of at least one of the above means; these tension constraints are less than 2 cN / tex at each entry of the three means set out above (regeneration, washing and drying) for a large number of tests: C-2 to C-5, C-10 to C- 11, C-13 to C-14, C-16 to C-23;
• the residence times in the regeneration means are of the order of 15 s, as in the washing means, while they are of the order of 10 s in the drying means;
• at the outlet of the drying means, the fibers have a residual moisture content of the order of 12% to 13% (% by weight of dry fiber).
  

A measure of the degree of substitution, as indicated in paragraph I-2.2, has shown that all of the fibers in Table 3 have a D _S value of between 0 and 2%, in the vast majority of cases between 0.1 and 1% .

As for the previous results, all the mechanical properties indicated in Table 3 are average values calculated over 10 measurements, at the exception of the title (average over 3 measures), the standard deviation on these different averages (in% of the average) generally being between 1 and 2.5%.

• T_E > 60 ;
• M_I > 1000 ;
• A_R > 6 ;
• E_R > 17,5 .

It can be seen that the regenerated fibers of Table 3 verify all of the following relationships:

• T _E >60;
• M _I >1000;
• A _R >6;
• E _R > 17.5.

Preferably, their elongation at break A _R is greater than 7% (examples C-4 to C-11, C-13 to C-16, C-19 and C-20), even more preferably greater than 8% (example C-4).

The best elongation value at break (A _R = 8.4% for test C-4) was notably obtained by spinning and online regeneration of a solution containing 16% by weight of cellulose and whose DP was about 420. The corresponding formate fiber sample, taken at the spinning outlet to measure the mechanical properties, showed the following properties:
Ds = 40; Te = 60; Mi = 1290; Ar = 8.4; Er = 25.3.

Furthermore, the vast majority of the fibers in Table 3 verify the following relationships:
T _E >80; M _I >1500; E _R > 25,
a large number of them verifying at least one of the following relationships:
T _E >100; M _I >2000; E _R > 30.

We note in particular particularly high tenacity (equal or greater than 100 cN / tex) in the case of tests C-1, C-7, C-18, C-21 and C-22, combined with high values of elongation and energy at break, or even even at high values of initial modulus, higher than 2400 cN / tex in the case of tests C-18, C-21 and C-22.

For all the examples in Table 3, we also note that the following relation is verified:
M _I <2600.

However, particularly high initial modulus values, for example between 2600 and 3000 cN / tex, are still accessible on fibers regenerated according to the invention, normally to the detriment of the elongation at failure, by adapting the parameters of the regeneration process according to the invention. This could be achieved in particular by increasing the constraints of tensions on the regeneration line, or by selecting fibers start (in cellulose formate) already presenting particularly values high initial modulus, for example between 1800 and 2200 cN / tex.

If for most of the examples in Table 3, the filamentary title (title of the fiber T _I divided by the number N of filaments) is equal to approximately 1.8 dtex (decitex) (most common filamentary title for cellulosic fibers) , the latter can vary to a large extent, for example from 1.4 dtex to 4.0 dtex, or even more, by adjusting the spinning conditions in known manner. By way of example, the regenerated fibers of tests C-19 and C-20 have, respectively, a filamentary titer of 2.9 dtex and 3.6 dtex. In general, an increase in elongation at break A _R has been observed, combined with a decrease in the tenacity TE and in the initial modulus M _I , when the filamentary title increases.

B) Fibers not in accordance with the invention (table 4):

A total of 9 regeneration tests of cellulose formate fibers are carried out. (referenced from D-1 to D-9), according to a regeneration process not in accordance with the invention.

The regeneration conditions are the same as those used for the fibers in accordance with the invention of table 3 above, with one exception: the environment regenerating agent is an aqueous sodium hydroxide solution whose concentration of sodium hydroxide Cs is at most equal to 16%.

Table 4 gives both the specific conditions for carrying out the process of the invention, and the properties of the fibers obtained. The abbreviations and the units used in this table 4 are the same as for the previous table 3.

All the fibers obtained are well regenerated, insofar as, after control, the values of degree of substitution D _S are always less than 2%, more precisely between 0.1% and 1.0%.

These fibers of Table 4 may have particularly high characteristics of toughness and initial modulus (see in particular D-7 to D-9), but it can be seen that none of them is in accordance with the invention, the relationship following is not verified:
A _R > 6.

In Examples D-4 and D-5 (Cs = 6% and 12%), we observed in particular a partial dissolution on the surface of the filaments, leading to the presence of married filaments, with a poor general condition of the fiber resulting in very large difficulties in performing a neutral wash. In example D-6, the same phenomena have been encountered, but to a lesser degree: we are here at the limits of the process of the invention (Cs = 16%), and there is in particular an elongation at the break very close to 6%.

A comparison of examples D-3 and C-12 (Table 3) turns out to be quite interesting, insofar as the regeneration operations have been carried out on the same cellulose formate fiber and, except for the concentration in sodium hydroxide of the regenerating medium (3% for test D-3, 30% for test C-12), under strictly identical special conditions.

It is indeed observed that compared to a conventional regeneration with a weakly concentrated soda solution (test D-3), the process of the invention (test C-12) made it possible to very significantly improve the toughness values (18% increase), elongation at break (33% increase), energy at break (55% increase), without any significant change in the initial module value.

All the fibers of tables 1 to 4 above, in cellulose formate or in regenerated cellulose, whether or not they conform to the invention, have a typical structure and morphology of products spun from a liquid crystal solution, as described in particular in basic application WO 85/05115.

In particular, when studying their filaments with an optical microscope or a scanning electron microscope, we observe a morphology such that each filament is constituted at least in part by layers nested one in the others surrounding the axis of the filament; we also note that in each layer, general, the optical direction and the crystallization direction vary almost periodically along the axis of the filament. Such a structure or morphology is described commonly in the literature under the name of "band structure".

C) Other properties of regenerated cellulose fibers according to the invention - Use in pneumatics:

In addition to the improved mechanical properties described above, the fibers of regenerated cellulose of the invention have many other advantages when compared to the fibers described in basic application WO 85/05115 aforementioned on the one hand, to conventional fibers of the rayon type on the other hand.

C-1. Comparison with regenerated cellulose fibers according to WO 85/05115:

Compared with the fibers described in basic application WO 85/05115, the fibers of the invention in particular have a very high fatigue strength appreciably improved, both in laboratory test and in pneumatic rolling.

Compression endurance (laboratory test):

For technical fibers, intended in particular to reinforce structures tires, the fatigue resistance can be analyzed by submitting assemblies of these fibers in various known laboratory tests, including the fatigue test known as the "Disc Fatigue Test" (see for example US 2,595,069, standard ASTM D885-591 revised 67T).

This test well known to those skilled in the art (see for example US 4,902,774) essentially consists in incorporating twists of the fibers to be tested, previously glued, in rubber blocks, then, after cooking, tire the gum test pieces thus formed in compression, between two rotating discs, a very large number of cycles (for example between 100,000 and 1,000,000 cycles). After fatigue, the twists are extracted from test pieces and their residual breaking strength is compared to the breaking strength twisted witnesses extracted from non-tired test pieces.

The fibers of the invention, compared to the fibers of the basic application WO 85/05115, systematically show markedly improved endurance in the "Disc Fatigue Test".

By way of example, fibers according to the invention having an elongation at preferential breaking greater than 7%, as well as fibers according to the application WO 85/05115 all having an elongation at break less than 5%, were assembled to form plied (type "A" and "B", respectively) having the same formula 180x2 (tex) 420/420 (t / m).

In known manner, such a formula means that each ply consists of two yarns (multifilament fibers), each having a count of 180 tex before twisting, which are first of all twisted individually at 420 rpm in one direction during a first step, then twisted the two together at 420 rpm in the opposite direction during a second step. For such a plied twist, the helix angle is approximately 27 ° and the coefficient of torsion (or torsional factor) K is approximately 215, with: K = Twisted twist (in t / m) x [Twisted title (in tex) / 1520] ½ . (cellulose density: 1.52)

• retors type "A" : 25 à 40 ;
• retors type "B" : 70 à 100 .

Several twists of type "A" (according to the invention) and of type "B" (according to WO 85/05115) were subjected to the "Disc Fatigue Test" above (6 hours at 2700 cycles / min, with a rate maximum compression of the test piece by approximately 16% in each cycle); the following force-breaking lapses were recorded on the extracted twists (data in relative values, with a base 100 for the maximum lapsing recorded on a type “B” plied):

• plied type "A": 25 to 40;
• plied type "B": 70 to 100.

The fatigue resistance of the regenerated fibers of the invention is therefore significantly improved - by a factor of two to three on average - compared with the regenerated fibers of the initial application WO 85/05115.

Tire endurance:

The ability of technical fibers to reinforce tires can be analyzed, in a known manner, by reinforcing a sheet of rubber with twists of the fibers to be tested, previously glued, incorporating the fabric thus formed in a tire structure, for example in a carcass ply reinforcement, and then subjecting the tire as well reinforced with a rolling test.

Such rolling tests are widely known to those skilled in the art, they can for example be implemented on automatic machines allowing to vary a large number of parameters (pressure, load, temperature ...) during driving. After rolling, the twists are extracted of the tire tested, and their residual breaking strength is compared to that control plies extracted from control tires which have not undergone the rolling.

It has been found that the fibers of the invention, when used for reinforce a radial tire carcass, show endurance which is significantly improved compared to fibers according to WO 85/05115. In in particular, it has been observed that where fibers according to the prior art do not not resist (rupture of the twisted type "B" above), due to particularly severe driving conditions, the fibers of the invention (devious type "A" above) showed almost no lapse, even after tens of thousands of kilometers.

C-2. Comparison with conventional rayon type fibers:

In addition to their significantly higher mechanical properties in extension, the regenerated fibers of the invention have other characteristics quite apart from advantageous fact. compared to conventional rayon fibers.

Moisture resistance:

The moisture resistance of cellulosic fibers can be analyzed using various known tests, a simple test consisting for example of soaking the fibers completely in a water bath, for a determined time, then measure the breaking strength of the fibers in the wet state, by pulling them immediately out of the water bath after simply having them drained.

After 24 hours of storage in water at room temperature, it is found that the breaking strength in the wet state, for the fibers of the invention, represents 80 to 90%, depending on the case, of the nominal breaking force (ie in the dry, measured as indicated in paragraph 1-4.). For rayon fibers, it now only represents around 60% of the nominal breaking force.

The fibers of the invention are therefore much less sensitive to moisture than conventional rayon fibers, they have better dimensional stability in a humid environment.

Mechanical properties on plied:

The fibers of the invention can be assembled, as described previously, to form reinforcement assemblies at high or very high mechanical properties, in particular plies whose construction can be adapted to a very large extent depending on the intended application. We know for example that an increase in torsion, i.e. of the helix angle, generally improves the endurance of the plied, increases its elongation at break, while being however detrimental to its toughness and its extension module.

Even for very high twists, corresponding for example to an angle 29-30 ° helix, which gives excellent twists endurance properties, the fibers of the invention, in the twisted state, have a toughness which is still greater than the toughness of fibers radiates not twisted.

By way of example, the plies according to the invention, prepared according to known twisting methods from the fibers of the invention, present, when the twisted helix angle is varied from 20 to 30 degrees, a toughness which can vary from 75-80 cN / tex up to 45-50 cN / tex, for example a toughness of the order of 58-66 cN / tex for a helix angle of 23-24 ° (K = 180 approximately), or 53-57 cN / tex for a helix angle of 26-27 ° (K = 215 approximately), as well as an elongation at break which can reach values close to 10% or even higher.

Thus, the toughness of the plies according to the invention, at equivalent torsion (same helix angle), are generally much greater than toughness on plies obtainable from rayon type fibers whose toughness hardly exceeds, in a known manner, 45-50 cN / tex before twisting. We can therefore use them in smaller quantities in articles usually reinforced with conventional rayon fibers.

Tire endurance:

For real driving conditions, implemented on vehicles of tourism fitted with 165/70 R 13 tires, we found unexpectedly that fibers of the invention (despite a structure significantly more rigid and more crystallized since they come from a phase liquid crystal), revealed throughout rolling tests (for example checks every 5,000 km, from 20,000 to 80,000 km) endurance identical to that of a conventional rayon fiber, for a construction identical twists.

Extension modules:

The fibers of the invention, the primary characteristic of which is a improved elongation at break, have an initial modulus which remains all very high (for example approximately 1500 to 2600 cN / tex in Table 3), in all cases very clearly superior to that of rayon fibers conventional (approximately 1000 cN / tex, in known manner).

This superiority of the fibers of the invention in terms of modulus, which is of course found on the reinforcement assemblies of these fibers, can be quite beneficial for reinforced items usually by conventional technical fibers, offering such articles the possibility of improved dimensional stability: indeed, for the same variation Δ (F) of the load or force "F" acting on a assembly of each type, the assembly according to the invention will undergo a significantly less variation Δ (A) in length or elongation "A".

In conclusion, a comparison of the results of the invention with those described in the WO 85/05115, both for cellulose formate fibers and for regenerated cellulose fibers, shows that the invention has not only enabled very significantly increase the elongation at break values, which are more than doubled in some cases but still maintain the toughness values at a very high standard, or even improve them in many cases.

The advantage of such a result must be particularly emphasized.

The improvement brought by the invention does not consist in a simple displacement towards another optimum of a given combination [tenacity-elongation at break], with an energy at break remaining substantially the same (total surface under the curve of Force-Elongation traction remaining substantially constant); it actually consists of a very noticeable improvement in any combination [toughness-elongation at rupture], allowing in a way to "extend" the Force-Elongation curves obtained for the fibers of the initial application WO 85/05115, and thus to obtain a very markedly improved energy at break (increased surface area under the curve Force-Elongation).

Of course, the invention is not limited to the examples previously described.

Thus, for example, different constituents can possibly be added with the basic constituents previously described (cellulose, formic acid, acid phosphoric, acetone, soda), without the spirit of the invention being modified.

This is how the term "cellulose formate" used in this document covers cases where the hydroxyl groups of the cellulose are substituted by groups other than the formate groups, in addition to these, for example ester groups, in particular acetate groups, the degree of substitution of cellulose for these other groups being preferably less than 10%.

The additional constituents, preferably chemically non-reactive with the basic constituents, can be for example plasticizers, sizes, dyes, polymers other than cellulose which may be esterified during the making of the solution. It can also be various additives making it possible, for example, to improve the spinability of spinning solutions, properties of use of the fibers obtained, the adhesiveness of these fibers to a matrix of rubber.

The invention also covers the cases where a chain consisting of one or more is used. several non-cylindrical capillaries, of various shapes, for example from a single slit-shaped capillary, the term "fiber" used in the description and claims should then be understood in a more general sense, which may include especially the case of a cellulose formate film or a cellulose film regenerated.

Claims (27)

1. Fibre made of cellulose formate, characterised by the following relationships:

   Ds ≥ 2;

   Te > 45;

   Mi > 800;

   Ar > 6;

   Er > 13.5,

   Ds being the degree of substitution of the cellulose with formate groups (in %), Te being its tenacity in cN/tex, Mi being its initial modulus in cN/tex, Ar being its elongation at break in % and Er being its energy at break in J/g.
2. Fibre according to Claim 1, characterised by the following relationship:
      Ar > 7.
3. Fibre according to Claim 2, characterised by the following relationship:
      Ar > 8.
4. Fibre according to any one of Claims 1 to 3, characterised by the following relationships:
      Te > 60; Mi > 1200; Er > 20.
5. Fibre according to Claim 4, characterised by at least one of the following relationships:
      Te > 70; Mi > 1500; Er > 25.
6. Method for spinning an optically anisotropic solution of cellulose formate in a solvent based on phosphoric acid, according to the so-called dry-jet-wet spinning method, in order to obtain a fibre in accordance with any one of Claims 1 to 5, characterised in that the stage of coagulation of the fibre and the stage of neutral washing of the coagulated fibre are both carried out in acetone.
7. Method according to Claim 6, characterised in that the temperature of the coagulation acetone is negative and in that the temperature of the washing acetone is positive.
8. Method according to Claim 7, characterised in that the following relationships exist:
      Tc < -10°C; Tl > +10°C, Tc being the temperature of the coagulation acetone and Tl being the temperature of the washing acetone.
9. Method according to any one of Claims 6 to 8, characterised in that at least one of the following characteristic is satisfied:

   a) the amount of residual solvent in the fibre, at the outlet of the coagulation means (recorded as Rs), in less than 100% by weight of dry fibre;

   b) the tensile stress undergone by the fibre at the outlet of the coagulation means (recorded as σ_c) is less than 5 cN/tex.
10. Method according to Claim 9, characterised by the following relationships:
       Rs < 50%; σ_c < 2 cN/tex.
11. Method according to any one of Claims 6 to 10, characterised in that the spinning solution exhibits at least one of the following characteristics:

    its cellulose concentration is between 15% and 25%;

    its total formic acid concentration is between 10% and 25%;

    its phosphoric acid concentration is between 50% and 75%;

    the degree of substitution of the cellulose with formate groups is between 25% and 50%;

    the degree of polymerisation of the cellulose is between 350 and 600;

    it contains less than 10% water.
12. Fibre made of cellulose regenerated from cellulose formate, characterised by the following relationships:

    0 < D_s < 2;

    T_E > 60;

    M_I > 1000;

    A_R > 6;

    E_R > 17.5,

    D_s being the degree of substitution of the cellulose with formate groups (in %), T_E being its tenacity in cN/tex, M_I being its initial modulus in cN/tex, A_R being its elongation at break in % and E_R being its energy at break in J/g.
13. Fibre according to Claim 12, characterised by the following relationship:
       A_R > 7.
14. Fibre according to Claim 13, characterised by the following relationship:
       A_R > 8.
15. Fibre according to any one of Claims 12 to 14, characterised by the following relationships:
       T_E > 80; M_I > 1500; A_R > 25.
16. Fibre according to Claim 15, characterised by at least one of the following relationships:
       T_E > 100; M_I > 2000; A_R > 30.
17. Method for the production of a fibre made of regenerated cellulose in accordance with any one of Claims 12 to 17 by passing a fibre made of cellulose formate according to any one of Claims 1 to 5 into a regenerating medium, washing and then drying, characterised in that the regenerating medium is an aqueous sodium hydroxide solution in which the sodium hydroxide concentration, recorded as Cs, is greater than 16% (% by weight).
18. Method according to Claim 17, characterised in that the following relationship exists:
       Cs > 18%.
19. Method according to Claim 18, characterised in that the following relationship exists:
       22% < Cs < 40%.
20. Method according to Claim 19, characterised in that the following relationship exists:
       22% < Cs < 30%.
21. Method according to any one of Claims 17 to 20, characterised in that the tensile stresses undergone by the fibre at the inlet of the regeneration means, of the washing means and of the drying means are less than 10 cN/tex.
22. Method according to Claim 21, characterised in that the tensile stresses are less than 5 cN/tex.
23. Method according to any one of Claims 17 to 22, characterised in that it is used in line and continuously with the method in accordance with any one of Claims 6 to 11.
24. Reinforcing assembly comprising at least one fibre made of cellulose formate according to any one of Claims 1 to 5 and/or at least one fibre made of regenerated cellulose according to any one of Claims 12 to 16.
25. Article reinforced by at least one fibre made of cellulose formate according to any one of Claims 1 to 5 and/or at least one fibre made of regenerated cellulose according to any one of Claims 12 to 16 and/or at least one assembly according to Claim 24.
26. Article according to Claim 25, characterised in that it is a tyre.
27. Tyre according to Claim 26, characterised in that its carcass reinforcement is reinforced by a fibre made of cellulose formate according to any one of Claims 1 to 5 and/or at least one fibre made of regenerated cellulose according to any one of Claims 12 to 16 and/or at least one assembly according to Claim 24.