FR3039550A1 - METHOD FOR MANUFACTURING RUBBER COMPOSITION BASED ON NATURAL RUBBER. - Google Patents

Abstract

The present invention relates to a method for manufacturing a rubber composition based on at least one natural rubber and a reinforcing filler, which process comprises the following steps (a) and (b): • (a) adding to a fresh natural rubber field latex a substance selected from the group consisting of proteases, surfactants and mixtures thereof, to produce a treated latex; (b) removing water from the natural rubber. The process according to the invention makes it possible to prepare a rubber composition based on at least natural rubber and a reinforcing filler which has a reduced hysteresis without degradation of its limiting properties.

Description

The present invention relates to a method of manufacturing a rubber composition based on natural rubber.

Natural rubber is an elastomer very widely used in the field of pneumatics because of its remarkable properties. For example, it is used in rubber compositions for the manufacture of semi-finished for vehicles carrying heavy loads, because of the compromise of performance that it can bring to the tire. Indeed, the introduction of natural rubber into a rubber composition reinforced by a reinforcing filler such as a carbon black or a silica gives the rubber composition a very interesting compromise in terms of hysteresis and cohesion which results in terms of performance for the tire by a good compromise between rolling resistance, endurance and tire wear.

The natural rubber used as elastomer in the rubber compositions comes from the rubbery solids of the natural rubber latex, very often extracted from the rubber tree. It is generally recovered according to two major processes. The first is based on the coagulation of spontaneous natural rubber in the bottom of the cup from field latex, the second on coagulation of the field latex with the aid of a chemical agent, preceded or not by centrifugation of the latex generally. stabilized. The unitary steps which constitute each of the processes are far from having no effect on the final chemical composition of the natural rubber, in particular on the macromolecular structure of the polyisoprene. It is therefore known to those skilled in the art that the chosen preparation process can very strongly impact the properties of natural rubber and therefore those of rubber compositions based on natural rubber.

Moreover, there are numerous published works dealing with natural rubber treatments, for example in its latex form, such as the elimination of proteins or lipids from natural rubber (respectively deproteinization or delipidation in English), the functionalization of polyisoprene chains. These treatments are also described to modify the properties of natural rubber, and hence the properties of rubber compositions based on natural rubber.

However, it is still a constant concern to improve the properties of rubber compositions based on natural rubber in order to increase the performance of tires comprising such compositions.

Continuing their efforts, the Applicants have discovered that a method of specific preparation of a rubber composition based on at least natural rubber and a reinforcing filler makes it possible to reduce the hysteresis of the rubber composition without degrading its limiting properties. ; this method has the particularity of comprising the addition to a fresh natural rubber field latex of a substance selected from the group consisting of proteases, surfactants and their mixture, to produce a treated latex.

Thus, a first object of the invention is a method for preparing a rubber composition based on at least one natural rubber and a reinforcing filler, characterized in that it comprises the steps (a) and ( b) the following: • (a) the addition to a fresh natural rubber field latex of a substance selected from the group consisting of proteases, surfactants and mixtures thereof, to produce a treated latex, • (b) water removal from natural rubber.

The present invention also relates to the use of a natural rubber in a rubber composition which comprises a reinforcing filler, which natural rubber is prepared by a process comprising steps (a) and (b). The invention also relates to the use of natural rubber in a rubber component for a tire, which natural rubber is prepared by a process comprising steps (a) and (b). I. DETAILED DESCRIPTION OF THE INVENTION

By the term "composition-based" is meant a composition comprising the mixture and / or the reaction product of the various constituents used, some of these basic constituents being capable of or intended to react with one another, less in part, during the various phases of manufacture of the composition, in particular during its crosslinking or vulcanization.

By the term "part by weight per hundred parts by weight of elastomer" (or phr), is meant within the meaning of the present invention, the mass part per hundred parts of elastomer present in the rubber composition considered.

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are percentages (%) by mass. On the other hand, any range of values designated by the expression "between a and b" represents the range of values from more than a to less than b (i.e. terminals a and b excluded) while any range of values designated by the term "from a to b" means the range from a to b (i.e., including the strict limits a and b).

In the present application, by natural rubber field latex is meant the latex resulting from the bleeding rubber tree. In the remainder of the description, the term field latex refers to natural rubber field latex. A field latex is an aqueous dispersion comprising several species that can be classified into two families: the natural rubber elastomer present in particle form and the non-rubbery compounds.

In the present application, natural rubber is understood to mean the elastomeric part of the natural rubber latex.

In the present application, by fresh field latex is meant a field latex which has not undergone the maturation phenomenon, also known as the fermentation of the latex. Latex maturation is a phenomenon well known to those skilled in the art and refers to an evolution of the field latex which occurs after bleeding under the effect of bacteriological or enzymatic actions, which would be caused by the contamination of the latex by microorganisms naturally present in the plantation environment. The addition of the substance being carried out on a fresh field latex, the skilled person understands that this addition is done before the coagulation of the latex.

Preferably, the fresh field latex is a latex which has been harvested at the latest the day after bleeding. In other words, the addition of the substance is carried out at the field latex no later than 1 day after the day of bleeding.

More preferably, the fresh field latex is a latex which has been collected at the latest the day of bleeding. In other words, the substance is added to the field latex on the day of the bleeding.

Even more preferably, a container for collecting the bleeding latex contains the substance from the moment the latex flows into the container or alternatively before the latex flows.

The substance is selected from the group consisting of proteases, surfactants and mixtures thereof.

According to a first variant, the substance is a protease. This variant makes it possible to achieve the best hysteresis gains of the rubber composition.

According to a second variant of the invention, the substance is a surfactant. This variant makes it possible to reduce the hysteresis while offering an improved compromise between the implementation of the rubber composition and its hysteresis.

According to a third variant of the invention, the substance is a mixture of a protease and a surfactant. This variant makes it possible to reduce the hysteresis while offering an improved compromise between the properties at break and the hysteresis of the rubber composition. As a protease, any enzyme capable of breaking peptide bonds, especially those present in the field latex, is suitable. Examples that may be mentioned include acid proteases, neutral proteases and alkaline proteases, in particular papain. Preferably, the protease is papain. As surfactant, mention may be made of any surfactant, whether anionic, nonionic or amphoteric, especially those mentioned in patent application EP 624 601. Thus, the anionic surfactants include sulphates, sulphonates, carboxylates, especially of fatty acids, phosphates; among nonionic surfactants, polyethers, among amphoteric surfactants, amino acids, betaines. Preferably, the surfactant is a sulfate, more preferably sodium dodecyl sulfate (SDS).

According to a preferred embodiment of the invention, the substance is used in the form of a dispersion, preferably an aqueous dispersion. The use of a dispersion of the substance allows a better contact of the substance with the latex and facilitates the handling of the substance, and ultimately increases the efficiency of the process from the point of view of the amount of the added substance. The concentration of the substance in the aqueous dispersion of the substance is not a critical element in the process. It may be chosen by those skilled in the art so as to optimize the aqueous dispersion volume of the substance to be added to the latex relative to the volume of latex to be treated, taking into account in particular the viscosity of the dispersion.

The amount of the substance used should be sufficient to observe an effect on the hysteresis of the natural rubber-reinforced rubber composition. Typically, the level of added substance is at least 0.01 g per 100 g of natural rubber. The maximum amount of the substance that can be used is usually limited for economic reasons. This is why the rate of the substance generally does not exceed 5 g per 100 g of natural rubber. Thus the level of the substance added to the latex preferably varies in a range from 0.01 g to 5 g per 100 g of natural rubber, more preferably from 0.1 to 3 g per 100 g of natural rubber.

In the present application, the terms "treated natural rubber latex" or "treated latex" are used interchangeably to denote the natural rubber latex resulting from step a).

The treated latex can then be subjected to different unit operations depending on the intended application of the natural rubber, particularly depending on the form in which the natural rubber will be used. Indeed natural rubber can be used in the form of latex, for example for applications in glues or in the solid state, for example in the form of natural rubber ball.

The treated latex resulting from step (a) contains, in particular, water coming from the field latex and, if appropriate, from the aqueous dispersion. Natural rubber is generally dried before being used in a rubber composition, in particular prior to incorporation of the reinforcing filler into the natural rubber. The water removal step is an operation widely practiced by those skilled in the field of the manufacture of natural rubber, in particular for use in a tire rubber composition. It can be done by drying under atmospheric air or an inert gas, such as nitrogen, or under vacuum. The vacuum drying can be carried out under a stream of an inert gas, such as nitrogen or in the presence of air. Drying is preferably carried out at a moderate temperature, especially at a temperature of at most 80 ° C, for example from room temperature (23 ° C) to 80 ° C.

According to a first variant, the elimination of water is carried out when the natural rubber is still in the latex state, for example directly on the treated latex.

According to a second variant, the elimination of water is carried out on a coagulum resulting from the coagulation of the treated latex.

Preferably, the removal of water is conducted on a coagulum resulting from the coagulation of the treated latex.

The drying of the coagulum can be conducted under the drying conditions traditionally used in the machining plants (in English "remilling factory") of natural rubber, used in particular in the manufacture of grades TSR or RSS. In this respect, drying is possible under the sole action of the ambient air, with or without smoking (respectively "air drying" and "smoke drying"), drying in machines such as tunnel-type dryers.

The coagulation of the treated latex may be spontaneous, for example in the container (called cup in English) for collecting the fresh field latex at the bleeding. The spontaneous coagulation of the mixture proceeds from the same principle as the spontaneous (or so-called natural) coagulation of well-known field latexes to give the cup-top (in English "cup lumps"), raw material of grades TSR20.

The coagulation of the treated latex may be caused by the addition of an additive, as for example this is traditionally done in refining plants of natural rubber, in particular to produce grades TSR3L and RSS. The coagulation additives of natural rubber latexes are well known to those skilled in the art. By way of example, mention may be made of metal ions, carboxylic acids and alcohols.

The so-called non-spontaneous coagulation, that is to say by adding an additive, is generally carried out on a stabilized latex. Therefore, the method according to the invention may comprise after step a) and before the step of removing water a step c) of stabilizing the treated latex. Step c) is a unitary operation widely practiced by those skilled in the field of the manufacture of natural rubber, in particular grades TSR3L and RSS, to avoid spontaneous coagulation of the latex and thus maintain the state of the art. latex.

According to one embodiment of the process according to the invention, step c) is carried out in a manner identical to that which is traditionally used in machining plants to stabilize field latices. Step c) therefore consists in maintaining the pH of the treated latex at a value greater than the isoelectric point of the field latex. Typically, the latex thus stabilized has a pH of at least 7, preferably around 9. This stabilization step may consist in adding a base to the latex. Preferably, the first base is added as an aqueous solution. As first base is suitable for example ammonia, sodium hydroxide or potassium hydroxide, preferably ammonia, more preferably a solution of ammonia in water.

Prior to the water removal step, the natural rubber whether in the form of coagulum or in the form of latex may be antioxidized by adding an antioxidant after step a). This particular embodiment is preferred when the drying is carried out in the presence of air or oxygen, in particular at temperatures of at least 60 ° C.

The polyisoprene chains of the natural rubber resulting from step a) may be subjected to treatments known to those skilled in the art which are the following: i. the functionalization of the polyisoprene chains of natural rubber, ii. stabilizing the viscosity of the natural rubber with an additive such as, for example, hydroxylamine or one of its salts, with a compound having a hydrazide function CONHNH2, iii. the dilution of the latex or, on the contrary, the concentration of the latex, in particular by centrifugation, by creaming (in English "creaming") or by evaporation.

Steps i, ii or iii) can be carried out on the polyisoprene chains after step a), but before step b) or for some of them after step b). They can also be performed after step c) of stabilization. They are conducted according to methods well known to those skilled in the art.

The natural rubber prepared by a process comprising steps a) and b) is used in a rubber composition which comprises a reinforcing filler.

The rubber composition is typically prepared by incorporating the reinforcing filler into the natural rubber prepared by a process comprising steps a) and b), especially by kneading, more particularly by thermomechanical kneading.

The composition of the invention comprises any type of so-called reinforcing filler known for its ability to reinforce a rubber composition that can be used for the manufacture of tires, for example an organic filler such as carbon black, a reinforcing inorganic filler such as silica to which is associated in a known manner a coupling agent, or a mixture of these two types of filler. Such a reinforcing filler typically consists of nanoparticles whose average size (in mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm.

Preferably, the content of total reinforcing filler (carbon black and / or reinforcing inorganic filler such as silica) is between 20 and 200 phr, more preferably between 30 and 160 phr, more preferably from 30 to 90 phr. optimum being in a known manner and different according to the particular applications targeted: the level of reinforcement expected on a bicycle tire, for example, is of course less than that required on a tire capable of driving at high speed in a sustained manner, for example a tire motorcycle, a tire for a passenger vehicle or for a commercial vehicle such as a heavy truck.

Suitable carbon blacks are all carbon blacks, especially blacks conventionally used in tires or their treads (so-called pneumatic grade blacks). Among these, the reinforcing carbon blacks of the 100, 200, 300 series or the 500, 600, 700 or 900 series blacks (ASTM grades), for example the blacks N115, N134, N234, N326, are particularly suitable. , N330, N339, N347, N375, N550, N683, N772). These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a carrier for some of the rubber additives used.

"Reinforcing inorganic filler" means any inorganic or mineral filler, irrespective of its color and origin (natural or synthetic), also called "white" filler, "clear" filler or even "non-black" filler. as opposed to carbon black, capable of reinforcing on its own, without any other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words able to replace, in its function reinforcement, a conventional carbon black of pneumatic grade; such a filler is generally characterized, in known manner, by the presence of hydroxyl groups (-OH) on its surface.

Suitable reinforcing inorganic fillers are in particular mineral fillers of the siliceous type, preferentially silica (SiO 2). The silica used may be any reinforcing silica known to those skilled in the art, especially any precipitated or fumed silica having a BET surface and a CTAB specific surface area both of less than 450 m 2 / g, preferably between 60 and 300 m 2 / g-A highly dispersible precipitated silica (called "HDS") include, for example, the "Ultrasil" 7000 and "Ultrasil" 7005 silicas from Degussa, the "Zeosil" 1165MP, 1135MP and 1115MP silicas from Rhodia , the "Hi-Sil" silica EZ150G from the PPG company, the "Zeopol" 8715, 8745 and 8755 silicas from the Huber Company, the high surface area silicas as described in the application WO 03/016387. In the present disclosure, the BET surface area is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" Vol. 60, page 309, February 1938, specifically according to the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: time at 160 ° C - relative pressure range p / po: 0.05 at 0.17). The CTAB specific surface is the external surface determined according to the French standard NF T 45-007 of November 1987 (method B).

In order to couple the reinforcing inorganic filler to the diene elastomer, an at least bifunctional coupling agent (or bonding agent) is used in a well-known manner to ensure a sufficient chemical and / or physical connection between the inorganic filler (surface of its particles) and the diene elastomer. In particular, organosilanes or at least bifunctional polyorganosiloxanes are used.

In particular, polysulfide silanes, called "symmetrical" or "asymmetrical" silanes according to their particular structure, are used, as described, for example, in claims WO 03/002648 (or US 2005/016651) and WO 00/002649 (or US 2005/016650).

In particular, polysulphide silanes having the following general formula (I) are suitable, but not limited to: (I) ZA-Sx-AZ, wherein: x is an integer of 2 to 8; preferably from 2 to 5); the symbols A, which may be identical or different, represent a divalent hydrocarbon radical (preferably a C 1 -C 18 alkylene group or a C 6 -C 12 arylene group, more particularly a C 1 -C 10, especially C 1 -C 4, alkylene, in particular propylene); the symbols Z, identical or different, correspond to one of the three formulas below:

in which: the radicals R1, substituted or unsubstituted, which are identical or different from one another, represent a C1-C18 alkyl, C5-C18 cycloalkyl or C6-C18 aryl group (preferably C1-C6 alkyl groups), cyclohexyl or phenyl, especially C1-C4 alkyl groups, more particularly methyl and / or ethyl). the radicals R2, substituted or unsubstituted, which are identical to or different from each other, represent a C 1 -C 18 alkoxyl or C 5 -C 18 cycloalkoxyl group (preferably a group chosen from C 1 -C 8 alkoxyls and C 5 -C 8 cycloalkoxyls, more preferentially still another group selected from C 1 -C 4 alkoxyls, in particular methoxyl and ethoxyl).

The content of coupling agent is advantageously less than 20 phr, it being understood that it is generally desirable to use as little as possible. Typically the level of coupling agent is from 0.5% to 15% by weight relative to the amount of inorganic filler. Its level is preferably between 0.5 and 12 phr, more preferably in a range from 3 to 10 phr. This level is easily adjusted by those skilled in the art according to the level of inorganic filler used in the composition.

The rubber composition may furthermore comprise all or part of the usual additives normally used in elastomer compositions intended to constitute mixtures of finished articles of rubber such as tires, in particular treads, such as, for example, plasticizers. or extender oils of aromatic or nonaromatic nature, pigments, protective agents such as antiozone waxes, chemical antiozonants, anti-oxidants, anti-fatigue agents, reinforcing resins (such as resorcinol or bismaleimide), acceptors (for example phenolic novolac resin) or methylene donors (for example HMT or H3M) as described, for example, in application WO 02/10269, a crosslinking system based on either sulfur or donors sulfur and / or peroxide and / or bismaleimides, vulcanization accelerators or retarders, vulcanization activators.

The rubber composition may contain, in addition to the natural rubber resulting from the process according to the invention, another diene elastomer. By "diene" elastomer (or indistinctly rubber) is to be understood in known manner an elastomer consisting at least in part (ie, a homopolymer or a copolymer) of monomeric diene units (monomers carrying two carbon-carbon double bonds, conjugated or not). As an elastomer, mention may be made of those conventionally used in the tire, such as polybutadienes (BR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers.

According to any of the embodiments of the invention, the rubber composition can be manufactured in mixers using two successive preparation phases well known to those skilled in the art: a first phase of work or thermomechanical mixing (phase so-called "non-productive") at high temperature, up to a maximum temperature of between 110 ° C and 200 ° C, preferably between 130 ° C and 185 ° C, followed by a second mechanical working phase (so-called "Productive") to a lower temperature, typically less than 120 ° C, for example between 40 ° C and 100 ° C, finishing phase during which is incorporated a crosslinking system. By way of example, the first (non-productive) phase is carried out in a single thermomechanical step during which all the constituents of the rubber composition are introduced into a suitable mixer such as a conventional internal mixer. exception of the crosslinking system. The total mixing time, in this non-productive phase, is preferably between 2 and 10 min. After cooling the mixture thus obtained during the first non-productive phase, the low temperature crosslinking system is then incorporated, generally in an external mixer such as a roll mill; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

The first kneading step is generally carried out by incorporating the reinforcing filler with the elastomer, in this case natural rubber and, if appropriate, other diene elastomers, in one or more times by thermomechanically kneading. In the case where the reinforcing filler, in particular carbon black, is already incorporated wholly or partly into the elastomer in the form of a masterbatch, it is the masterbatch which is directly kneaded and, if appropriate, incorporates other elastomers or reinforcing fillers present in the composition which are not in the form of masterbatch, as well as additives other than the crosslinking system.

The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for a characterization in the laboratory, or else extruded in the form of a rubber profile that can be used, for example, as a tread. tire for passenger vehicle.

The rubber composition may be in the green state (before crosslinking) or in the fired state (after crosslinking).

The rubber composition may be used in a tire, especially as a composition of one of the constituent elements of the tire. These constituent elements may be a rubber component such as a tread, a sheet or a filling compound.

The aforementioned features of the present invention, as well as others, will be better understood on reading the following description of several embodiments of the invention, given by way of illustration and not limitation.

II. EXAMPLES OF CARRYING OUT THE INVENTION II-1. Preparation of the rubber compositions: 4 rubber compositions C1, C2, C3 and C4 are prepared according to the process described below with the content of the constituents expressed in phr in Table I:

In an internal mixer (final filling rate: about 70% by volume), the initial temperature of the tank is approximately 80 ° C., successively the natural rubber elastomer, the reinforcing filler, and the various other ingredients. with the exception of the vulcanization system. Thermomechanical work (non-productive phase) is then carried out in one step, which lasts a total of about 3 to 4 minutes, until a maximum temperature of "fall" of 165 ° C is reached. The mixture thus obtained is recovered, cooled and then sulfur is incorporated and the sulfenamide type accelerator on a mixer (homo-finisher) at 70 ° C., mixing the whole (productive phase) for a suitable time (for example 3 hours). at 4 minutes).

The compositions are then calendered in the form of a plate with a thickness ranging from 2 to 3 mm or thin rubber sheets for the measurement of their physical or mechanical properties.

The rubber compositions differ in the nature of the natural rubber used in the rubber composition. The rubber compositions C1, C2, C3 and C4 respectively contain natural rubbers NR1, NR2, NR3 and NR4. All natural rubbers come from the same fresh field latex.

The NR1 natural rubber, taken as a control, comes from a coagulum recovered 3 days after the day of the bleeding, which was subjected to the following treatment: granulation after 5 passes in a crepe and 1 passage in a shredder, - then drying in air at 125 ° C.

NR1 natural rubber is a conventional grade TSR20.

The natural rubbers NR2, NR3 and NR4 are prepared differently from NR1 in that a protease, a surfactant and a mixture of protease and surfactant are respectively in the cup which collects the fresh field latex and which also contains 150 ml of water. . The protease is papain (Aldrich, reference P3375), the surfactant sodium dodecyl sulfate (SDS, Aldrich, reference 05030). The rate of papain introduced into the cup is 0.7% by mass of natural rubber, the SDS content of 0.3% by mass of natural rubber. The mixture of protease and surfactant is such that papain and SDS represent respectively 0.7% by weight of natural rubber and 0.3% by mass of natural rubber.

The rubber composition C1 is a control rubber composition, since it contains as a natural rubber a guard TSR20; the rubber compositions C2, C3 and C4 are rubber compositions prepared according to the process according to the invention, since the natural rubbers NR2, NR3 and NR4 have undergone the operations (a) and (b) of the process according to the invention. invention. 11-2. Results:

For each of the compositions vulcanized at 150 ° C., the Mooney plasticities, the properties at break, the modules, as well as the dynamic properties under the test conditions described below are measured.

The composition Cl is taken as a control. With the exception of the plasticity values, the values measured in each of the tests are expressed in base 100 relative to the values of the control composition. A value greater than 100 indicates a value greater than that of the control. The values measured in base 100 are shown in Table II.

Mooney plasticity (MS) of natural rubbers and rubber compositions:

An oscillating consistometer is used as described in the French standard NF T 43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the raw composition (i.e., before firing) is molded in a cylindrical chamber heated to 100 ° C. After a minute of preheating, the rotor (of small size) rotates within the test tube at 2 revolutions / minute and the useful torque is measured to maintain this movement after 4 minutes of rotation. Mooney plasticity (MS 1 + 4) is expressed in "Mooney unit" (UM, with 1 UM = 0.83 Newton.meter).

Traction tests:

The tensile tests make it possible to determine the elastic stress and the properties at break. Unless otherwise indicated, they are carried out in accordance with the French standard NF T 46-002 of September 1988. Traction data processing also makes it possible to draw the modulus curve as a function of elongation. The nominal secant modulus calculated at the initial elongation of the test specimen (or apparent stress, in MPa) at 100% and 300% elongation noted MSA100 and MSA300 respectively is measured at first elongation. The breaking stresses (in MPa) and the elongations at break (in%) are measured at 60 ° C.

Dynamic Properties

The loss factor tan (δ) max is measured on a viscoanalyzer (Metravib VA4000) according to ASTM D 5992-96. The response of a sample of vulcanized composition (in the form of 2 test pieces 2 mm thick and 10 mm in diameter) is recorded, subjected to sinusoidal stress in alternating simple shear, at the frequency of 10 Hz, at 60 °. C according to ASTM D 1349-99. A strain amplitude sweep is performed from 0.1% to 50% (forward cycle) and then from 50% to 0.1% (return cycle). The result exploited is the loss factor tan (δ). For the return cycle, the maximum value of tan (δ) observed, denoted tan (δ) max, is indicated.

The C2, C3 and C4 rubber compositions made according to the process according to the invention are less hysteretic than the control composition, without there being a substantial change in the breaking properties and the modules.

It is noted that: the strongest hysteresis decrease is obtained when the substance is a protease, papain; the best compromise between the hysteresis and the implementation is obtained when the substance is a surfactant, SDS; the best compromise between the properties at break and the hysteresis when the substance is a mixture of a protease and a surfactant, respectively papain and SDS.

Table I

(1) "Wingstay 100" (mixture of N, N '- (phenyl and tolyl) benzene-1,4-diamines), (2) N-1,3-dimethylbutyl N-phenyl-para-phenylenediamine (3) N-cyclohexyl-2 benzothiazylsulfenamide

Table II

Claims (14)

A method of manufacturing a rubber composition based on at least one natural rubber and a reinforcing filler, characterized in that it comprises the following steps (a) and (b): (a) adding to a fresh natural rubber field latex a substance selected from the group consisting of proteases, surfactants and mixtures thereof, to produce a treated latex; (b) removing water from the natural rubber. 2. The method of claim 1 wherein the addition of the substance is carried out at the latest 1 day after the day of bleeding. 3. Method according to any one of claims 1 to 2 wherein the addition of the substance is carried out at the latest the day of the bleeding. A method according to any one of claims 1 to 3 wherein a container for collecting the fresh field latex which is flowing at the bleed contains the substance from the moment the latex flows or alternatively before the latex does not flow. 5. Process according to any one of claims 1 to 4 wherein the substance is in the form of a dispersion, preferably aqueous. 6. Method according to any one of claims 1 to 5 the level of the added substance is in a range from 0.01 g to 5 g per 100 g of natural rubber, preferably from 0.1 to 3 g per 100 g of rubber natural. 7. Process according to any one of claims 1 to 6 wherein the step (b) of removing water is performed on the treated latex. 8. Process according to any one of claims 1 to 6 wherein step (b) is carried out on a coagulum originating from the coagulation of the treated latex. 9. A process according to any one of claims 1 to 8 wherein the substance is a protease, preferably papain. 10. Process according to any one of claims 1 to 8 wherein the substance is a surfactant, preferably an anionic surfactant, more preferably a sulfate. 11. A process according to any one of claims 1 to 8 wherein the substance is a mixture of a protease and a surfactant, preferably a mixture of papain and anionic surfactant, more preferably a mixture of papain and a sulphate. 12. Method according to any one of claims 1 to 11 wherein it comprises the incorporation of the reinforcing filler in the natural rubber, preferably by kneading, more preferably by thermomechanical kneading. Use of a natural rubber in a rubber composition which comprises a reinforcing filler, which natural rubber is prepared according to steps (a) and (b) as defined in any one of claims 1 to 11. 14. Use of a natural rubber in a tire rubber component, which natural rubber is prepared according to steps (a) and (b) as defined in any one of claims 1 to 11.