WO2015097196A2

WO2015097196A2 - Rubber composition containing cellulose fibers

Info

Publication number: WO2015097196A2
Application number: PCT/EP2014/079086
Authority: WO
Inventors: Didier Vasseur; Olivia Cuscito
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2013-12-23
Filing date: 2014-12-22
Publication date: 2015-07-02
Also published as: FR3015497B1; WO2015097196A3; FR3015497A1

Abstract

The invention relates to a reinforced rubber composition consisting of at least one diene elastomer, of one or more inorganic reinforcing fillers, and of cellulose fibers, in which: said cellulose fibers have a length of 0 to 300 µm; at least 50 wt% of said cellulose fibers have a length of 70 to 130 µm; said cellulose fibers have a thickness of 0.3 µm to 1.5 µm; and said cellulose fibers have a mean thickness of 0.3 µm to 1.1 µm.

Description

Rubber composition comprising cellulose fibers

The invention relates to a reinforced rubber composition based on a diene elastomer, a reinforcing filler and cellulosic fibers of particular dimensions, as well as to a process for the preparation of such a composition, to a semi-finished article and a tire containing it.

Since fuel savings and the need to preserve the environment have become priorities, it is desirable to produce mixtures with as little hysteresis as possible while possessing good wear resistance properties so that they can be processed in the best possible manner. implement in the form of rubber compositions usable for the manufacture of various semi-finished products used in the tire composition, such as for example treads, in order to obtain tires having improved rolling resistance without penalization resistance to wear.

Ideally, for example, a tire tread must meet a large number of frequently conflicting technical requirements, including high wear resistance while providing the tire with low rolling resistance and high adhesion. on so dry as on so wet, snowy or icy.

To improve the wear resistance, it is known, a certain rigidity of the tread is desirable, this stiffening of the tread can be obtained for example by increasing the rate of reinforcing filler, with a significant surface area or by incorporating certain reinforcing resins into the constituent rubber compositions of these treads.

Unfortunately, experience shows that the improvement of the rolling resistance properties, which is accompanied by a decrease in the hysteretic losses of the rubber composition, penalizes in a known manner, the stiffening of the tread. Improving rolling resistance performance by maintaining good rigidity is therefore a constant concern for tire designers.

There is therefore a permanent need to provide a rubber composition which makes it possible to obtain tires having improved rolling resistance without penalizing the wear resistance.

In view of the foregoing, it is a general object to provide rubber compositions which satisfy a compromise of stiffness / hysteresis properties acceptable for tire use.

The Applicants have discovered that a reinforced rubber composition based on at least one diene elastomer, at least one reinforcing inorganic filler and cellulose fibers, wherein:

said cellulo fibers have a length ranging from 10 to 300 μπι,

at least 50% by weight of said cellulose fibers have a length ranging from 70 to 130 μιη,

said cellulose fibers have a thickness varying from 0.3 μιη to 1.5 μιη,

said cellulosic fibers have an average thickness ranging from 0.3 μιη to 1.1 μιη

allowed to obtain improved hysteretic properties while maintaining a good level of rigidity.

The object of the invention is therefore to provide a reinforced rubber composition based on at least one diene elastomer, at least one reinforcing inorganic filler and cellulosic fibers, in which:

said cellulos fibers have a length varying from

10 to 300 μπι,

at least 50% by weight of said cellulose fibers have a length ranging from 70 to 130 μιη, said cellulose fibers have a thickness varying from 0.3 μηι to 1.5 μηι,

said cellulosic fibers have an average thickness ranging from 0.3 μιη to 1.1 μπι.

The invention also relates to a method for preparing a rubber composition for the manufacture of tires as defined above, comprising the following steps:

- Incorporating into said diene elastomers or, in a first step, said reinforcing inorganic fillers and cellulosic fibers, by thermomechanically kneading the whole, in one or more times, until reaching a maximum temperature between 1 10 ° C and 1 90 ° C;

- Then incorporate, in a second step, a crosslinking system and knead the whole to a maximum temperature of less than 1 10 ° C, preferably less than 80 ° C.

The invention also relates to a semi-finished rubber tire article comprising such a cross-linkable or cross-linked rubber composition.

The invention finally relates to a tire incorporating such a semi-finished article.

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are% by weight. 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 (that is, the excluded terminals a and b) while that any range of values designated by the expression "from a to b" means the range of values from a to b (that is, including the strict limits a and b).

"Composition based on" means 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 at least in part. during the various phases of manufacture of the composition, in particular during its crosslinking or vulcanization. As explained above, the rubber composition according to the invention is based on one or more diene elastomers.

By diene elastomer, it is to be understood in a known manner (is meant one or more) elastomer derived at least in part (ie, a homopolymer or a copolymer) of monomers dienes (monomers bearing two carbon-carbon double bonds, conjugated or not ). More particularly, diene elastomer is any homopolymer obtained by polymerization of a conjugated diene monomer having 4 to 12 carbon atoms, or any copolymer obtained by copolymerization of one or more conjugated dienes with one another or with one or more vinylaromatic compounds. having from 8 to 20 carbon atoms. In the case of copolymers, these contain from 20% to 99% by weight of diene units, and from 1 to 80% by weight of vinylaromatic units.

As conjugated dienes that can be used in the process according to the invention, 1,3-butadiene, 2-methyl-1,3-butadiene and 2,3-di (C ₁ -C ₅ ) alkyl-1 are especially suitable. 3-butadiene such as, for example, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl 3-isopropyl-1,3-butadiene, phenyl-1,3-butadiene, 1,3-pentadiene and 2,4-hexadiene, etc.

Examples of suitable vinylaromatic compounds are styrene, ortho-, meta, para-methylstyrene, the commercial "vinyltoluene" mixture, para-tert-butylstyrene, methoxystyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene, and the like.

The diene elastomer of the composition in accordance with the invention is preferably chosen from the group of highly unsaturated diene elastomers consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR) and butadiene copolymers. , in particular copolymers of butadiene and a vinyl aromatic monomer, isoprene copolymers and mixtures of these elastomers.

Among butadiene copolymers, butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), copolymers of isoprene-styrene (SIR) and copolymers of isoprene-butadiene-styrene (SBIR). As explained above, the composition according to the invention is also based on one or more reinforcing fillers and cellulose fibers.

As reinforcing inorganic filler, is meant by the present application, by definition, any inorganic or inorganic filler whatever its color and its origin (natural or synthetic), capable of reinforcing on its own, without any other means than an agent intermediate coupling, a rubber composition for the manufacture of tires; 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 siliceous mineral fillers or aluminous mineral fillers.

Among the siliceous mineral fillers, mention may be made of silica (SiO 2). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET surface and a CTAB specific surface both less than 450 m ² / g, preferably from 30 to 400 m ² / g, especially between 60 and 300 m2 / g.

Among the aluminous inorganic fillers, mention may be made of alumina (Al 2 O 3) or aluminum (oxide) hydroxides, or reinforcing titanium oxides, for example described in US 6 61 0 261 and US 6 747 087.

The physical state in which the reinforcing inorganic filler is present is indifferent whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term "reinforcing inorganic filler" also refers to mixtures of different reinforcing fillers, in particular highly dispersible siliceous fillers as described above.

As explained above, the cellulosic fibers contained in the composition according to the invention are such that: they have a length ranging from 10 to 300 μηι,

at least 50% by weight of them have a length ranging from 70 to 130 μιη,

they have a thickness varying from 0.3 μιη to 1.5 μιη, they have an average thickness ranging from 0.3 μιη to

1, 1 μπι.

According to a preferred embodiment, at least 50% by weight of the cellulosic fibers have a length ranging from 90 to 10 μπι.

According to another preferred mode, combinable with the above, the cellulose fibers have an average thickness ranging from 0.9 to 1.1 μπι.

Thus, the cellulose fibers present in the composition according to the invention have on average advantageously a form factor (length / thickness ratio) high, of the order of 100. This high form factor makes it possible to percolate a 3 D network. that is, the fibers form a three-dimensional network in which the distances between the fibers are short enough for interactions to develop. This makes it possible to obtain a rigid structure.

Preferably, the cellulose fibers represent from 10 to 50 phr, more preferably from 20 to 40 phr.

More preferably, the reinforcing inorganic filler (s) and the cellulose fibers represent a total of 40 to 1 phr.

According to a particularly preferred embodiment, the rubber composition according to the invention comprises a coupling agent.

Indeed, it is possible that the reinforcing inorganic filler or the cellulose fibers require the use of a coupling agent to establish the bond between the reinforcing inorganic filler or the cellulose fibers and the elastomer.

When the silica is present in the composition as a reinforcing filler, it is possible to use, as coupling agents, organosilanes, especially polysulphurized alkoxysilanes or mercaptosilanes, or at least bifunctional polyorganosiloxanes.

In the rubber composition according to the invention, the level of coupling agent is advantageously less than 20 phr, it being understood that it is generally desirable to use as little as possible. Its rate is preferably between 0, 5 and 12 phr. The presence of the coupling agent depends on that of the reinforcing inorganic filler or cellulosic fibers. Its rate is easily adjusted by the skilled person according to the rate of this charge; it is typically of the order of 0.5% to 15% by weight relative to the amount of reinforcing inorganic filler.

The rubber composition according to the invention may also contain, in addition to the coupling agents, coupling activators, charge-recovery agents or, more generally, processing aid agents which can be used in known manner, thanks to an improvement of the dispersion of the filler in the rubber matrix and a lowering of the viscosity of the composition, to improve its ability to use in the green state, these agents being for example the hydrolysable silanes such as alkylalkoxysilanes, polyols, polyethers, primary, secondary or tertiary amines, hydroxylated or hydrolyzable polyorganosiloxanes.

The rubber composition according to the invention may also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of tires, for example pigments, non-reinforcing fillers, protective agents such as waxes anti-ozone, anti-chemical ozonants, anti-oxidants, anti-fatigue agents, plasticizing agents, reinforcing or plasticizing resins, acceptors (eg novo lacquer phenolic resin) or methylene donors (eg HMT or H3M) as described for example in the application WO 02/1 0269, a crosslinking system that can be based on either sulfur, or sulfur and / or peroxide donors and / or bismaleimides, vulcanization accelerators or some vulcanization activators such as zinc oxide, stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine), N-cyclohexyl-2-benzothiazyl sulfenamide (abbreviated "CB S").

The rubber composition according to the invention is manufactured in suitable mixers, generally using two successive preparation phases according to a general procedure well known to those skilled in the art: a first working phase or thermomechanical mixing (sometimes referred to as "non-productive" phase) at a high temperature, up to a maximum temperature of between 1 10 ° C and 190 ° C, preferably between 1 15 ° C and 170 ° C and even more preferably between 1 15 ° C and 160 ° C ° C, followed by a second phase of mechanical work (sometimes referred to as a "productive" phase) at a lower temperature, typically below 1 10 ° C, for example between 30 ° C and 100 ° C, finishing phase during from which can be incorporated the crosslinking system.

Thus, according to the invention, the composition according to the invention is prepared according to the process comprising the following steps:

- Incorporating into said diene elastomers or, in a first step, said reinforcing inorganic fillers and cellulosic fibers, by thermomechanically kneading the whole, in one or more times, until reaching a maximum temperature between 110 ° C and 190 ° C;

According to a preferred embodiment of the invention, all the basic constituents of the composition used according to the invention, with the exception of the crosslinking system, namely the reinforcing inorganic fillers or the cellulose fibers, coupling agent, if appropriate, are intimately incorporated, by kneading, with the diene elastomer or the diene elastomers during the first so-called non-productive phase, that is to say that one introduces into the mixer and which is thermomechanically kneaded, in one or several steps, at least these various basic constituents until the maximum temperature of between 1 10 ° C and 190 ° C, preferably between 1 15 ° C and 170 ° C and even more preferably between 1 15 ° C and 160 ° C.

By way of example, the first (non-productive) phase is carried out in a single thermomechanical step in the course of which all the necessary constituents, the possible stabilizing agents, are introduced into a suitable mixer such as a conventional internal mixer. implementation complementary and other various additives, with the exception of the crosslinking system. The total mixing time in this non-productive phase is preferably between 1 and 15 minutes. 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 2 and 15 min.

As an alternative to mixing the elastomer and the dry phase fillers as described above, the mixture of the diene elastomer, the reinforcing filler (s) and the cellulosic fibers can also be carried out in the liquid phase. For this purpose, a latex elastomer is used which is in the form of elastomer particles dispersed in water, and an aqueous dispersion of the filler, that is to say a filler dispersed in water. , commonly called "slurry". Certain processes in particular, such as those described in US Pat. No. 6,048,923, make it possible to obtain a masterbatch of elastomer and filler having a very good dispersion of the filler in the elastomeric matrix.

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 as a tire tread for passenger car or truck.

As explained above, the invention is further concerned with a semi-finished tire rubber article comprising a crosslinkable or crosslinked rubber composition according to the invention.

As explained above, the invention is further obj and a tire comprising a semi-finished article according to the invention.

Due to the improvement of the hysteretic properties which characterize a reinforced rubber composition according to the invention, without deteriorating the rigidity, it will be noted that a tire whose tread comprises the composition has a rolling resistance advantageously increased without penalizing the wear resistance.

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.

Examples

Measurements and tests used

Dynamic Properties

The dynamic properties G * and tan (δ) max are measured on a viscoanalyzer (Metravib VA4000) according to ASTM D 5992-96. The response of a sample of vulcanized composition is recorded (cylindrical specimen 4 mm thick and 400 mm ² section), subjected to a sinusoidal solicitation in alternating simple shear, at a frequency of 10 Hz and at a measurement temperature of 60 ° C. A strain amplitude sweep of from 0.1% to 100% peak-to-peak (forward cycle) is performed, followed by 100% to 0.1% peak-to-peak (return cycle). The results exploited are the complex dynamic shear modulus (G *) and the loss factor tan (δ). For the return cycle, the maximum value of tan (δ) observed, denoted tan (δ) max, is indicated. This value is representative of the hysteresis of the material and in this case the rolling resistance: the higher the value of tan (δ) max is low, the lower the rolling resistance. The values of G * measured at 60 ° C are representative of the rigidity, that is to say of the resistance to deformation: the higher the value of G *, the greater the rigidity of the material, and therefore the resistance high wear.

Example 1

Two compositions according to the invention comprising a reinforcing inorganic filler and cellulose fibers (compositions B and C) are compared with a control composition containing carbon black (composition A).

The formulations of the compositions are given in Table 1. The amounts are expressed in parts per 100 parts by weight of elastomer (phr).

Table 1

(1) natural rubber

(2) SSBR (styrene-butadiene copolymer in solution) with 15.5% styrene, 48% polybutadiene units 1-4trans (mol%)

(4) SSBR with 26.5% styrene, 50% polybutadiene units 1-4trans

(mol%)

(5) BR with 98.4% cis polybutadiene units (mol%)

(6) Silica at 120 m ² / g

(7) Cellulose fibers marketed by JRS-Rettenmaier

(8) Liquid silane = bis (triethoxy) silane tetrasulfide

(9) 6-para-phenylenediamine

(10) Diphenyl guanidine (vulcanization accelerator)

(11) CBS: N-cyclohexyl-2-benzothiazyl sulfenamide ("Santocure CBS" from the company Flexsys)

(12) Zéosil 1165MP Silica from Rhodia

In an internal mixer (final filling ratio: approximately 70% by volume), the initial vessel temperature of which is approximately 60 ° C., the diene elastomers and, where appropriate, the carbon black or 2/3 weight of the silica. Thermomechanical work (non-productive phase) is then carried out in one step, which lasts a total of 5 minutes, during which the following compounds are introduced at the temperature of 95 ° C: stearic acid, ozone wax, plasticizer, 1/3 in weight of silica, Arbocel BWW40 and liquid silane until reaching a temperature of 165 ° C.

The mixture thus obtained is recovered, cooled and sulfur, diphenyl guanidine, ZnO and a sulfenamide type accelerator are incorporated on a mixer (homo-finisher) at 23 ° C., mixing everything (productive phase) for a suitable time (for example about ten minutes).

The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties.

The properties of the compositions in the crosslinked state are given in Table 2.

Table 2

The results show that the compositions B and C according to the invention have a high G * modulus and preserved relative to the comparative composition A, but with a very greatly reduced hysteresis, whatever the elastomer base of the mixture.

In other words, the stiffness / hysteresis compromise is improved.

It is well known that a decrease in hysteresis is favorable for the rolling resistance while the low deformation dynamic modulus will be favorable for the stiffness of the drifting tire and therefore a preserved road behavior.

Claims

1. A reinforced rubber composition based on at least one diene elastomer, one or more reinforcing inorganic fillers and cellulose fibers, wherein:

said cellulos fibers have a length varying from

10 to 300 μπι,

said cellulose fibers have a thickness varying from 0.3 μιη to 1.5 μιη,

2. Composition according to Claim 1, characterized in that the diene elastomer or elastomers are chosen from natural rubber, synthetic polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

3. Composition according to claim 1 or 2, characterized in that the reinforcing inorganic filler or fillers are chosen from siliceous mineral fillers, preferably silica, and aluminous mineral fillers, preferably alumina.

4. Composition according to any one of the preceding claims, characterized in that at least 50% by weight of said cellulose fibers have a length ranging from 90 to 1 10 μπι.

5. Composition according to any one of the preceding claims, characterized in that the cellulose fibers have an average thickness ranging from 0.9 to 1.1 μπι.

6. Composition according to any one of the preceding claims, characterized in that the cellulose fibers represent from 10 to 50 phr, preferably from 20 to 40 phr.

7. Composition according to any one of the preceding claims, characterized in that the inorganic filler (s) reinforcing and cellulose fibers total 40 to 1 10 phr.

8. Composition according to any one of the preceding claims, characterized in that it comprises a coupling agent.

9. Semi-finished rubber tire article, characterized in that it comprises a crosslinkable or crosslinked rubber composition as defined in any one of claims 1 to 8.

10. Pneumatic tire, characterized in that it comprises a semi-finished article as defined in claim 9.

1 1. Process for preparing a rubber composition for the manufacture of tires as defined in any one of Claims 1 to 8, characterized in that it comprises the following steps: