EP1179096B1 - Method for obtaining a carbon fiber fabric by continuous carbonization of a fabric consisting of cellulosic fibers - Google Patents

Abstract

The carbonization of cellulose fiber fabric comprises an initial stage of heat treatment up to 250° C. to 350° C., with a relatively high mean temperature rise speed of 10° C./min to 60° C./min, an intermediate stage up to 350° C. to 500° C. with a lower mean temperature rise speed of 2° C./min to 10° C./min, and a final stage up to 500° C. to 750° C. with a mean temperature rise speed that is again raised to 5° C./min to 40° C./min.

Description

Field of the invention

The invention relates to the manufacture of fabrics made of carbon from cellulosic cellulose fibers precursor carbon.

The invention aims more particularly, but not exclusively, the manufacture of carbon fiber fabric by carbonization of a fabric made of viscose fibers, especially rayon fibers.

Background of the invention

Cellulosic precursor carbon fibers exhibit generally a porous structure formed of turbostratic carbon very disorganized, this structure being further disoriented by relative to the axial direction of the fibers and their pore network.

These characteristics give carbon fibers a low thermal conductivity, which makes them particularly suitable for formation of thermal protective coatings, such as ablative coatings for combustion chambers and nozzles thrusters.

Other applications have been envisaged for the fabrics in cellulosic precursor carbon fibers, in particular the production of heating resistors, the production of battery electrodes or catalyst supports, or the formation of activated tissues used as adsorbent materials.

Processes for obtaining carbon fiber fabrics from Cellulosic precursor are known. We can refer in particular to US Patents 3,053,775, US 3,107,152, US 3,305,315 and US 3,663,173.

A commonly used method is to perform a direct carbonization of a cellulosic fiber fabric, especially a viscose fabric. The fabric is put in the form of a skein of a length from one to several hundred meters. It is precarbonized up to a temperature of about 400 ° C. Precarbonization is carried out in a container preferably in a neutral atmosphere, for example with nitrogen sweeping. Effluents from decomposition cellulose are sucked up and burned in a flare.

The rise in temperature is very slow, to respect the kinetics of decomposition of cellulose, in order to obtain a yield correct carbon, and to avoid a runaway of the reaction of decomposition, which is exothermic, such a runaway to annihilate the mechanical properties of the carbon fibers obtained. AT For example, for a skein of 100 meters, precarbonization can last up to 15 days, which is extremely long.

The pre-carbonization phase is followed by a treatment thermal at a temperature of about 1200 ° C for about 1 to 2 min. A final treatment at high temperature, for example 2800 ° C, can be done to increase the conductivity of the carbon and close its porosity.

A method and an installation for obtaining a fabric carbon fibers by continuous carbonization of a fiber fabric cellulosic, with a much lower heat treatment time long, are described in patents RU 2,005,829, UK 2,045,472 and UK 2,047,674.

The precursor fabric, for example viscose fibers is impregnated with an organosilicon compound which has the effect of maintain good mechanical properties for the fiber fabric of carbon obtained. The organosilicon compound is chosen from the compounds from the group of polydimethylphenylallylsilanes, polysiloxanes, polymethylsiloxanes, polysilazanes, polyalumino-organosiloxanes.

The impregnated fabric is subjected to heat treatment in continuous under air at a temperature between 100 ° C and 300 ° C, plus particularly between 100 ° C and 150 ° C, to induce relaxation of constraints that exist in cellulosic fibers and eliminate water adsorbed by the fibers.

The carbonization is then carried out on the moving fabric in continuously in an enclosure under an inert atmosphere, raising the temperature gradually to 300 ° C to 600 ° C. Treatment at high temperature, maximum up to 280 ° C under inert atmosphere, is then realized.

During carbonization, the gaseous effluents of pyrolysis of the cellulose are sucked up and burned in a flare, the suction means being located in the enclosure where the maximum of degradation of cellulose.

This process makes it possible to obtain mechanical properties satisfactory for carbon fibers, but leads to deformations of the resulting fabric, such as disorganization of weaving and embossing.

Such deformations are not acceptable, especially when the fabric is to be used for making part preforms made of composite material, because they lead to a heterogeneity of distribution of the fibers in the preform, which affects the behavior of the parts made of composite material reinforced by these fabrics.

Object and summary of the invention

The object of the invention is to avoid these drawbacks by proposing a process for obtaining carbon fiber fabric by carbonization of cellulosic fiber fabric, whereby a carbon fiber fabric obtained does not show any significant deformation.

• une phase initiale pour amener la température du tissu à une valeur comprise entre 250°C et 350°C, la phase initiale comprenant une montée en température à une première vitesse moyenne comprise entre 10°C/min et 60°C/min,
• une phase intermédiaire pour élever la température du tissu jusqu'à une valeur comprise entre 350°C et 500°C, la phase intermédiaire comprenant une montée en température à une deuxième vitesse moyenne inférieure à la première et comprise entre 2°C/min et 10°C/min, et
• une phase finale pour élever la température du tissu jusqu'à une valeur comprise entre 500°C et 750°C, la phase finale comprenant une montée en température à une troisième vitesse moyenne supérieure à la deuxième et comprise entre 5°C/min et 40°C/min.

This object is achieved by a method in which a continuously moving fabric is subjected in a carbonization chamber to a heat treatment comprising:

• an initial phase for bringing the temperature of the fabric to a value of between 250 ° C. and 350 ° C., the initial phase comprising a rise in temperature at a first average speed of between 10 ° C./min and 60 ° C./min,
• an intermediate phase for raising the temperature of the fabric to a value between 350 ° C and 500 ° C, the intermediate phase comprising a rise in temperature at a second average speed less than the first and between 2 ° C / min and 10 ° C / min, and
• a final phase to raise the temperature of the fabric to a value between 500 ° C and 750 ° C, the final phase comprising a rise in temperature at a third average speed greater than the second and between 5 ° C / min and 40 ° C / min.

The choice of this particular temperature profile during the carbonisation responds to the desire to find the best compromise between the quality of carbonization, which depends in particular the holding fiber mechanics, the appearance quality of the fabric, that is, the absence significant loading and respect of the warp / weft geometry, and the maintenance of production costs at an acceptable level.

When it is carbonized, a cellulose fiber yarn undergoes a significant withdrawal. It can reach 30 to 40% when the wire is free of any tension.

In the case of a fabric undergoing a carbonization process continuously, the withdrawal of the weft son is virtually free and therefore reaches almost the maximum value.

The removal of the weft threads between the inlet and the outlet of the the Chamber imposes a convergence (progressive approximation) of the chain. A favorable situation for obtaining a fiber fabric of carbon without excessive embossing and without deformation of geometry would the one where, along the path in the chamber, the shrinkage substantially affects in the same way the weft threads and the warp threads.

However, while each weft yarn is isothermal, the chain son that extend parallel to the scroll direction of the fabric in the room is not in isothermal. The temperature at which the same wire is exposed varies between its portion exposed to the lowest temperature, before entering the room and the portion exposed to the highest temperature, at the other end of bedroom.

In addition, while the removal of weft yarns is virtually free, that of the warp threads remains more or less slightly lower than the maximum possible value due to the inevitable tension on the warp threads by means of support and training of the fabric in continuous scrolling.

The temperature profile according to the method of the invention aims at answer a first concern, which is to induce on the weft threads a shrinkage to respect the geometry of the fabric during its withdrawal to avoid clogging or disruption of the fabric. Therefore, in an initial phase after entering the tissue into the enclosure, the elevation temperature is relatively fast, to impose an early withdrawal to the weft threads.

The temperature profile also aims to answer a second worry, which is to get a good mechanical quality of carbon threads resulting from carbonization. This is how, in a phase intermediate, where most of the decomposition of cellulose takes place, the temperature rise is slower to better respect the kinetics of decomposition. Choosing an average climb speed temperature between 2 ° C and 10 ° C can respond to this satisfactorily, without imposing a journey length excessive tissue.

The final stage of carbonization, which aims essentially at to give carbon the desired structure, can be conducted with again a faster temperature rise, most of the shrinkage in chain and weft have been observed, in order to reduce the total duration of the carbonization, so the production costs.

According to a particularity of the process, the fabric is scrolled in the carbonization chamber through successive zones in each of which reigns a controlled temperature.

According to another particularity of the method, the residence time of the tissue in the room is between 20 min and 2 h. Carbonization so is extremely fast.

According to yet another particularity of the process, the tissue, before carbonization, to a relaxation treatment at a temperature between 100 ° C and 250 ° C, preferably under air and for a duration for example between 15 min and 3 h.

Brief description of the drawings

• la figure 1 est une vue très schématique en coupe longitudinale d'une installation de carbonisation en continu pour l'obtention de tissus en fibres de carbone ;
• la figure 2 est une vue en coupe transversale selon le plan II-II de la figure 1 ;
• la figure 3 illustre une plage de profil thermique d'un tissu à l'intérieur d'une chambre de carbonisation selon un procédé conforme à l'invention ; et
• la figure 4 montre un tissu obtenu par mise en oeuvre d'un procédé autre que celui de l'invention.

Other features and advantages of the invention will become apparent on reading the description, given below by way of indication but not limitation, with reference to the accompanying drawings in which:

• Figure 1 is a schematic view in longitudinal section of a continuous carbonization plant for obtaining carbon fiber fabrics;
• Figure 2 is a cross-sectional view along the plane II-II of Figure 1;
• FIG. 3 illustrates a thermal profile range of a fabric inside a carbonization chamber according to a method according to the invention; and
• FIG. 4 shows a fabric obtained by using a method other than that of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A plant for the continuous carbonization of a fiber fabric Cellulosic is shown very schematically in Figure 1.

The carbonization is carried out on a fiber fabric T cellulose fibers, for example technical viscose fibers, to which added an organosilicon compound which acts, during the decomposition of the cellulose, so that the obtained carbon fibers retain good mechanical properties.

• celle des polyhydrosiloxanes, cycliques, linéaires ou ramifiés, substitués par des groupes méthyles et/ou phényles, dont la masse moléculaire moyenne en nombre est comprise entre 250 et 10 000, avantageusement entre 2 500 et 5 000 ; et
• celle des oligomères et résines, réticulés, cycliques ou ramifiés, qui présentent une masse moléculaire en nombre comprise entre 500 et 10 000 et qui sont constitués de motifs de formule SiO₄ (dits motifs Q₄) et de motifs de formule SiO_xR_y(OR')_z dans laquelle :
  • x, y et z sont des nombres entiers, tels que x + y + z = 4 et 1 ≤ x ≤ 3
             0 ≤ y ≤ 3
             0 ≤ z ≤ 3 ;
  • R représente l'hydrogène ou un radical alkyle, linéaire ou ramifié, comportant de 1 à 10 atomes de carbone, des R différents étant susceptibles d'intervenir dans un même motif, lorsque y ≥ 2 ;
  • R' représente, indépendamment de R, l'hydrogène ou un radical alkyle, linéaire ou ramifié, comportant de 1 à 10 atomes de carbone, des R' différents étant susceptibles d'intervenir dans un même motif, lorsque z ≥ 2 ;
  étant entendu que : - pour les oligomères qui présentent une masse moléculaire moyenne en nombre inférieure à 1 000, on a z # 0, dans ladite formule SiO_xR_y(OR')_z ; et
           - pour les résines qui présentent une masse moléculaire moyenne en nombre supérieure à 2 000, on a y # 0, dans ladite formule SiO_xR_y(OR')_z.

For this purpose, the viscose fabric T, in the dry state and freed of any size, is impregnated by passing through a bath containing said organosilicon compound in solution. As indicated above, the organosilicon compound may be selected from polysiloxanes. Preferably, a polysiloxane chosen from the families defined in the patent applications WO 01/42541 and WO 01/42544, these families being:

• that of cyclic, linear or branched polyhydrosiloxanes, substituted by methyl and / or phenyl groups, whose number-average molecular mass is between 250 and 10,000, advantageously between 2,500 and 5,000; and
• that of the oligomers and resins, crosslinked, cyclic or branched, which have a number-average molecular weight of between 500 and 10,000 and which consist of units of formula SiO ₄ (referred to as Q _{4 units} ) and units of formula SiO _x R _y (OR ') _z wherein:
  • x, y and z are integers, such that x + y + z = 4 and 1 ≤ x ≤ 3
    0 ≤ y ≤ 3
    0 ≤ z ≤ 3;
  • R represents hydrogen or an alkyl radical, linear or branched, having from 1 to 10 carbon atoms, different R being likely to occur in the same pattern, when y ≥ 2;
  • R 'represents, independently of R, hydrogen or a linear or branched alkyl radical containing from 1 to 10 carbon atoms, different R''s being capable of occurring in the same unit, when z ≥ 2;
  with the proviso that: - for oligomers which have a number average molecular weight of less than 1000, then az # 0 in said formula SiO _x R _y (OR ') _z ; and
  for resins having a number average molecular weight greater than 2,000, there is ## EQU1 ## in said formula SiO _x R _y (OR ') _z .

In particular, the organosilicon compound may be a siloxane resin, consisting of units of formula SiO ₄ (designated Q _{4 units} ), units of formula SiO ₃ -OH (so-called Q _{3 units} ) and units of formula O-Si-R ₃ (referred to as M units), advantageously consisting of n _{1 units} Q ₄ , n _{2 units} Q ₃ and n _{3 units} M, with 2 ≤ n ₁ ≤ 70, 3 ≤ n ₂ ≤ 50 and 3 ≤ n ₃ ≤ 50 and having a number average molecular weight of between 2,500 and 5,000.

The organosilicon compound may also be chosen from oligomers of a partially hydrolysed organic silicate, advantageously selected from oligomers of a partially alkyl silicate hydrolyzed, and preferably selected from oligomers of ethyl silicate partially hydrolysed.

The impregnation is carried out by scrolling the fabric T in a tray 10 containing the selected organosilicon compound, in solution in a solvent such as a chlorinated solvent (for example tetrachlorethylene) or acetone. Impregnation of the fabric can be achieved by passing through a bath (as illustrated) and / or by spraying the compound solution organosilicon on the faces of the fabric. At the outlet of the tray 10, the impregnated fabric is expressed by passing between rollers 12 in order to leave a controlled amount of compound.

The impregnated fabric is then admitted to a dryer 14 so to eliminate the solvent. The drying is carried out for example by air flow hot against the current of the fabric scrolling on embarrassments 16.

The impregnated and dried fabric is ready to be charred. he can be temporarily stored, for example by bambanning in a container or be admitted directly continuously to the carbonization station 18 itself.

It should be noted that the fabric may also have been impregnated with at least one mineral additive, acid or Lewis base, for example chosen from ammonium and sodium halides, sulphates and phosphates, urea and their mixtures and advantageously consists of in ammonium chloride (NH ₄ Cl) or diammonium phosphate [(NH ₄ ) ₂ HPO ₄ ].

The carbonization comprises a moderate heat treatment of drying and relaxation of the tissue followed by passage in an oven where the carbonization is actually carried out.

The relaxation treatment is performed by admission of the tissue in a chamber 20 at atmospheric pressure and in ambient air. The temperature in the chamber 20 is regulated to a value between 100 ° C and 250 ° C, for example about 130 ° C. The residence time in the enclosure 20 is preferably between 15 min and 3 h. The length of the path of the fabric in the enclosure, with passage on rolls of reference 22, is chosen to obtain the desired residence time depending the speed of scrolling of the fabric. Relaxation heat treatment allows a relaxation of the internal stresses of the cellulosic fibers, and removal of water adsorbed by the fabric.

The carbonization is then carried out by admission of the fabric in an enclosure 30 enclosing a carbonization chamber 40. The admission of the cellulosic fiber fabric into the chamber 40, at a end of it, and extracting the carbon fiber cloth out of the chamber 40, at the other end thereof, are made through sealing boxes 50, 52. At its entry into the box 50, the fabric is returned substantially at room temperature.

In the illustrated example, the carbonization chamber is a elongate chamber in which the fabric follows a horizontal straight path. Other configurations of the carbonization chamber may be considered, for example a room with several adjacent parts consecutive horizontal or vertical in which the fabric is guided by return rollers.

The chamber 40 is delimited by the horizontal walls 42 has lower and upper 42b, and vertical side walls 42 c, 42 d, for example of graphite. The chamber 40 is surrounded by an enclosure 30. Within the enclosure 30, electrical heating resistors 34 are arranged near the outer faces of walls 42 a, 42 b.

The interior of the chamber 40 is kept under atmosphere neutral, for example under nitrogen injected by pipes 36 respectively near the entrance and the exit of the room. of the products of decomposition of cellulose, during its carbonization, are extracts from the chamber through one or more chimneys 38. The extraction chimneys are placed at a level of the oven where occurs mainly the decomposition of cellulose. Extracted products can be flared (not shown).

Sealing boxes 50, 52 prevent access to the interior of chamber 40 by ambient air, which would have the effect of disturbing the circulation of the gases inside chamber 40 and oxidizing the fabric charred. Sealing boxes 50, 52 also prevent polluting leakage of decomposition products of cellulose in the shelter building the enclosure 30. It is advantageous to use, at least for the box 50, a combination of static sealing by inflatable bead contacting the fabric with a minimum of friction, and dynamic barrier sealing formed by injection of neutral gas. An embodiment of such a sealing box is described in the patent application WO 01/42542.

In cross-section, the carbonization chamber 40 has an elongated rectangular profile (FIG. 2). Between the inlet and the outlet of the chamber 40, the fabric passes through a succession of adjacent zones separated from each other by transverse walls 44 a, 44 b. The walls 44, for example graphite, are connected to top and side walls of the chamber 4, while the walls 44 b, for example also in graphite, are connected to the bottom and side walls of the chamber 40. The ends facing walls 44 a and 44 b define therebetween a slit 46 for the passage of the fabric.

The division of the chamber 40 into several consecutive zones 40 ₁ , 40 ₂ , 40 ₃ ,... Makes it possible to define different temperature zones between the inlet and the outlet of the chamber 40. In each zone, the temperature is regulated at a predetermined set value. For this purpose, the currents in the resistors 34 are regulated by a control circuit 46 on the basis of information provided by temperature probes 48 arranged in the different zones 40 ₁ , 40 ₂ , 40 ₃ , ....

• une phase initiale au cours de laquelle la température du tissu est amenée à une valeur comprise entre 250°C et 350°C, avec une montée en température du tissu à une première vitesse en moyenne comprise entre 10°C/min et 60°C/min,
• une phase intermédiaire au cours de laquelle la température du tissu est amenée jusqu'à une valeur comprise entre 350°C et 500°C, avec une montée en température du tissu à une deuxième vitesse en moyenne inférieure à la première et comprise entre 2°C/min et 10°C/min, et
• une phase finale au cours de laquelle la température du tissu est amenée à une valeur comprise entre 500°C et 750°C, la phase finale comprenant une montée en température à une troisième vitesse en moyenne supérieure à la deuxième et comprise entre 5°C/min et 40°C/min.

According to the invention, the temperatures in the different zones of the carbonization chamber are determined, as is the speed of travel of the fabric, a function of the length of said zones, so that the heat treatment applied to the fabric comprises:

• an initial phase during which the temperature of the fabric is brought to a value of between 250 ° C. and 350 ° C., with a rise in temperature of the fabric at a first average speed of between 10 ° C./min and 60 ° C. / min
• an intermediate phase during which the temperature of the fabric is brought to a value between 350 ° C and 500 ° C, with a rise in temperature of the fabric at a second speed on average less than the first and between 2 ° C / min and 10 ° C / min, and
• a final phase during which the temperature of the fabric is brought to a value of between 500 ° C. and 750 ° C., the final phase comprising a rise in temperature at a third speed on average greater than the second and of between 5 ° C. / min and 40 ° C / min.

The corresponding thermal profile range of the fabric is illustrated in Figure 3 in solid lines. In this FIG. 3, the curve C in mixed lines illustrates a "typical" profile.

The initial phase aims at imposing an early withdrawal of the frame fabric so that it adapts to the geometry of the warp yarns. In effect, while the weft yarns heat up progressively after their entering the carbonization chamber, the portion of each wire of chain entering the room is influenced by the part located in downstream exposed to a higher temperature. Imposing a rapid heating as soon as entering the chamber 40 allows the weft to "follow" the removal of the tissue and avoid the appearance of defects geometric in the fabric.

This is why a rate of temperature rise relatively fast is chosen. It is on average between 10 ° C / min and 60 ° C / min, preferably between 10 ° C / min and 40 ° C / min. The rate of rise in temperature may be higher at the beginning of the initial phase than at the end of it.

The tissue temperature at the end of the initial phase is included between 250 ° C and 350 ° C, preferably between 270 ° C and 300 ° C.

The intermediate phase is where most of the decomposition of cellulose. In order to keep fibers a good mechanical strength, this decomposition must be controlled, that is to say produce with a moderate rate of rise in temperature. In average, this speed is between 2 ° C / min and 10 ° C / min, preferably between 4 ° C / min and 6 ° C / min, being noted that too low a speed become economically disadvantageous.

The temperature of the tissue at the end of the intermediate phase is between 400 ° C and 450 ° C. This temperature is the temperature at which most of the decomposition of the cellulose is carried out.

The final phase is where the carbonization of the fibers is completed until the desired carbon structure is obtained.

The temperature of the fabric at the end of the final phase is included between 500 ° C. and 750 ° C., for example between 550 ° C. and 650 ° C. for reach a stage of charring sufficiently advanced.

During the final phase, the temperature rise can be faster than in the intermediate phase, since the decomposition of cellulose has been essentially achieved. In addition, the constraints related to differential withdrawals between string and frame are smaller since most of the shrinkage occurred in both the warp and weft. Speed average rise in temperature is chosen between 5 ° C / min and 40 ° C / min, for example between 25 ° C / min and 30 ° C / min.

A desired thermal profile for the tissue in the chamber of carbonization 40 is likely to be reproduced with even more that the number of zones in chamber 40 is high, with individual control of the temperature in each zone. In practice, the number of zones is at least 3, preferably at least equal to 6.

At the outlet of the sealing box 52, the fabric passes between call rollers 54 before being stored for example in the form of a coil 56. The call rollers are associated with means of training (not shown) to control the scrolling of the fabric at the desired speed. It should be noted that due to the removal of the warp threads during carbonization, the speed of entry of the fabric into the chamber 40 is greater than the output speed.

The residence time of the fabric in the chamber 40 is included between 20 minutes and 2 hours.

High temperature heat treatment can be realized on the carbonized fabric from the chamber 40. This heat treatment is performed continuously by passing the fabric in a furnace 60. This treatment thermal aims to achieve a structuring of carbon fibers. It is temperature above 1000 ° C, up to 2800 ° C, under a neutral atmosphere, for example under nitrogen. The weather of residence of the fabric in the oven 60 is preferably between 1 min and 10 min, for example about 2 min. The fabric is taken from the spool 56 and is stored, at the furnace outlet 60, on a coil 62, being called by rolls 64.

The carbon fabric directly from chamber 40 can also be carefully oxidized by exposure to water vapor or carbon dioxide, under conditions well known to elsewhere to obtain activated carbon fabric without heat treatment at high temperature.

Example 1

A carbonization plant with a shared chamber is used in 8 zones 40 ₁ to 40 ₈ of equal lengths.

Different strips of the same technical rayon fabric consisting of 3,600 dtex yarns with 11 threads / cm in warp and weft been carbonized in this installation after being impregnated by an organosilicon compound consisting of a resin polyhydromethylsiloxane marketed by the French company Rhodia Silicones under the reference "RHODORSIL RTV 141 B", and a treatment drying and relaxation at 170 ° C for 90 min.

Different controlled temperatures in the furnace zones and different running speeds were chosen so that the temperatures and the temperature rise rates of the fabric in the different zones of the carbonization chamber 40 are within the ranges indicated in the table below. -Dessous. The temperature limits are represented by dashed lines in FIG. 3. The total carbonization times ranged from 30 minutes to 70 minutes. Zoned 40 ₁ 40 ₂ 40 ₃ 40 ₄ 40 ₅ 40 ₆ 40 ₇ 40 ₈ Temp. (° C) 230 to 300 250 to 330 270 to 340 300 to 360 330 to 410 400 to 510 510 to 600 600 to 700 Average speed of rise in temp. (° C / min) 20 to 60 2 to 10 2 to 10 2 to 10 2 to 10 5 to 25 5 to 25 5 to 25

In this oven, the vent or chimneys for the decomposition products of the cellulose are located between the zones 40 ₅ and 40 ₆ .

In all cases, there is an absence of folds on the fabric at the outlet of the carbonization chamber, thanks to the thermal profile according to the invention.

After charring, the tissue was continuously treated at 1200 ° C under nitrogen for 90 s.

Tensile tests were performed on the various carbon fabric strips obtained. Values of between 30 and 70 daN / cm in a chain, and between 30 and 50 daN / cm in weft were measured for a fabric weight per m ² of between 310 and 330 g. At the level of the carbon filament, this corresponds to a breaking strength of between 1000 and 1300 MPa and a Young's modulus of between 30 and 50 GPa.

Comparative example

A rayon fiber fabric such as that of the examples above was carbonized continuously.

For comparison, the same fabric was charred in similar conditions with the exception of the char profile, the temperature rise of the fabric having been carried out at a speed constant 7 ° C / min from room temperature to 650 ° C.

FIG. 4 shows the embossed appearance of the fabric obtained, due to a offset of the withdrawal between the chain and the frame.

Claims (9)

1. A method of obtaining a carbon fibre fabric by continuously carbonising a cellulose fibre fabric, the method being characterised in that the fabric travelling continuously through a carbonisation chamber is subjected to heat treatment comprising:

   an initial stage for bringing the temperature of the fabric to a value lying in the range 250°C to 350°C, the initial stage comprising temperature rise at a first mean speed lying in the range 10°C/min to 60°C/min;

   an intermediate stage for raising the temperature of the fabric to a value lying in the range 350°C to 500°C, the intermediate stage comprising temperature rising at a second mean speed lower than the first and lying in the range 2°C/min to 10°C/min; and

   a final stage for raising the temperature of the fabric to a value lying in the range 500°C to 750°C, the final stage comprising temperature rising at a third mean speed greater than the second and lying in the range 5°C/min to 40°C/min.
2. A method according to claim 1, characterised in that the fabric is caused to travel through the chamber via successive zones, each of which has a controlled temperature therein.
3. A method according to claim 1 or claim 2, characterised in that the transit time of the fabric through the chamber lies in the range 20 min to 2 h.
4. A method according to claim 1 or claim 2, characterised in that, prior to carbonisation, the fabric is subjected to relaxation treatment at a temperature lying in the range 100°C to 250°C.
5. A method according to claim 4, characterised in that the relaxation treatment is performed in air.
6. A method according to claim 4 or claim 5, characterised in that the relaxation treatment is performed for a duration lying in the range 15 min to 3 h.
7. A method according to any one of claims 1 to 6, characterised in that the carbonised fabric is subjected to high temperature heat treatment lying in the range 1000°C to 2800°C after it has passed through the carbonisation chamber.
8. A method according to claim 7, characterised in that the high temperature heat treatment is performed for a duration lying in the range 1 min to 10 min.
9. A method according to any one of claims 1 to 6, characterised in that the carbonised fabric is subjected to activation treatment.

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