EP3810436A1

EP3810436A1 - Rubber composition comprising a specific crumb rubber

Info

Publication number: EP3810436A1
Application number: EP19737857.3A
Authority: EP
Inventors: Etienne Fleury
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2018-06-21
Filing date: 2019-06-13
Publication date: 2021-04-28
Also published as: CN112334322B; US20210171752A1; FR3082848B1; CN112334322A; WO2019243711A1; FR3082848A1

Abstract

The invention relates to a rubber composition based on at least one elastomer, a reinforcing filler, a cross-linking system and 5 to 100 phr of a crumb rubber, said crumb having a median size D50 of 100 to 300 µm, and a particle size distribution such that the ratio of the median sizes D10/D50 is greater than or equal to 0.5; said composition further comprising 1 to 10 phr of a tackifying resin having a number average molecular weight (Mn) of more than 800 g/mol and a polymolecularity index (Ip) greater than or equal to 2.0.

Description

RUBBER COMPOSITION COMPRISING A POWDER OF

SPECIFIC RUBBER

The invention relates to compositions, in particular for tires and more particularly to compositions comprising a rubber crumb.

Indeed, it is interesting today for tire manufacturers to find solutions to minimize the environmental impact of rubber compositions without penalizing the performance of tires using these compositions.

It is known in the state of the art that rubber crumbs can be used in tires. For example, document US 2014/0228505 describes the use of a rubber crumb of a size less than 60 mesh (250 μm) in compositions for tires.

However, the simple reduction in the size of the crumbs can lead to reduced sticky performance when raw, in particular during the manufacture of tires, in particular when they are present in large quantities.

Now, the Applicant has shown that a composition comprising a particular rubber crumb constitutes an effective recycling of vulcanized rubber materials, making it possible to obtain rubber compositions having a reduced environmental impact, and a very good tack. raw, allowing easier industrial implementation, especially for the manufacture of tires.

The invention therefore relates to a rubber composition based on at least one elastomer, a reinforcing filler, a crosslinking system and 5 to 100 phr of a rubber crumb, said crumb having an average size D50 included between 100 and 300 µm, and a particle size distribution such that the ratio of mean sizes D10 / D50 is greater than or equal to 0.5; said composition further comprising 1 to 10 phr of a tackifying resin having a number average molecular mass (Mn) greater than 800 g / mol and a polymolecularity index (Ip) greater than or equal to 2.0.

The invention also relates to a tire comprising a composition as defined above, preferably in all or part of its tread. Preferably, the tire according to the invention will be chosen from tires intended to equip a two-wheeled vehicle, a passenger vehicle, or even a so-called "heavy vehicle" (that is to say metro, bus , off-road vehicles, road transport equipment such as trucks, tractors, trailers), or even airplanes, civil engineering, agricultural or handling equipment.

I- Constituents of the composition

The rubber compositions according to the invention are based on at least one elastomer, a reinforcing filler, a crosslinking system and 5 to 100 phr of a rubber crumb, said crumb having an average size D50 included between 100 and 300 µm, and a particle size distribution such that the ratio of mean sizes D10 / D50 is greater than or equal to 0.5; said composition further comprising 1 to 10 phr of a tackifying resin having a number average molecular mass (Mn) greater than 800 g / mol and a polymolecularity index (Ip) greater than or equal to 2.0.

By the expression “composition based on” is meant a composition comprising the mixture and / or the in situ reaction product of the various basic constituents used, some of these constituents being able to react and / or being intended to react between them, at least partially, during the various stages of manufacturing the composition, or during subsequent cooking, modifying the composition as it is prepared at the start. Thus, the compositions as used for the invention may be different in the non-crosslinked state and in the crosslinked state.

Furthermore, the term "pce" means within the meaning of this patent application, part by weight per hundred parts of elastomers, within the meaning of the preparation of the composition before cooking. That is to say, in the case of the presence of a rubber crumb, that the term “pce” means part by weight per hundred parts of “new” elastomers, therefore excluding from the base 100 the elastomers contained in the rubber crumb.

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 going from more than a to less than b (ie limits a and b excluded) while any range of values designated by the expression "from a to b" means the range of values from a to b (that is to say including the strict limits a and b). When reference is made to a “majority” compound, it is understood within the meaning of the present invention, that this compound is predominant among the compounds of the same type in the composition, that is to say that it is that which represents the greatest quantity by mass among the compounds of the same type and in particular more than 50%, preferably more than 75%. Thus, for example, a majority polymer is the polymer representing the largest mass relative to the total mass of the polymers in the composition. Likewise, a so-called majority charge is that representing the largest mass among the charges of the composition. By way of example, in a system comprising a single polymer, this is in the majority within the meaning of the present invention; and in a system comprising two polymers, the majority polymer represents more than half of the mass of the polymers. On the contrary, a “minority” compound is a compound which does not represent the largest mass fraction among the compounds of the same type.

When reference is made to a “majority” unit (or monomer) within the same compound (or polymer), it is understood within the meaning of the present invention, that this unit (or monomer) is predominant among the units (or monomers) forming the compound (or polymer), that is to say it is that which represents the largest fraction, by mass among the units (or monomers) forming the compound (or polymer).

The compounds mentioned in the description can be of fossil origin or bio-based. In the latter case, they can be, partially or totally, from biomass or obtained from renewable raw materials from biomass. Are concerned in particular polymers, plasticizers, fillers, etc.

1-1 Elastomer

The elastomer can be chosen from the group consisting of diene elastomers and mixtures of these.

By elastomer (or "rubber", the two terms being considered synonymous) of the "diene" type, it is recalled here that must be understood in known manner an elastomer derived at least in part (ie, a homopolymer or a copolymer ) diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not). Diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". In general, the term "essentially unsaturated" means a diene elastomer derived at least in part from conjugated diene monomers, having a proportion of units or units of diene origin (conjugated dienes) which is greater than 15% (% by moles); This is how diene elastomers such as butyl rubbers or copolymers of dienes and of alpha-olefins of the EPDM type do not enter into the preceding definition and can be qualified in particular as “essentially saturated” diene elastomers (content of motifs of diene origin weak or very weak, always less than 15%). In the category of “essentially unsaturated” diene elastomers, the expression “highly unsaturated” diene elastomer is understood in particular to mean a diene elastomer having a rate of units of diene origin (conjugated dienes) which is greater than 50%.

These definitions being given, one means more particularly by diene elastomer capable of being used in the compositions according to the invention:

(a) any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

(b) any copolymer obtained by copolymerization of one or more dienes conjugated together or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms;

(c) a ternary copolymer obtained by copolymerization of ethylene, of an α-olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer having of 6 to 12 carbon atoms, such as for example the elastomers obtained from ethylene, of propylene with a non-conjugated diene monomer of the aforementioned type such as in particular hexadiene-1, 4, ethylidene norbornene, dicyclopentadiene;

(d) a copolymer of isobutene and isoprene (butyl rubber), as well as the halogenated, in particular chlorinated or brominated, versions of this type of copolymer.

Although it applies to any type of diene elastomer, a person skilled in the art of the tire will understand that the present invention is preferably implemented with essentially unsaturated diene elastomers, in particular of type (a). or (b) above.

By way of conjugated dienes, butadiene-1, 3, 2-methyl-1, 3-butadiene, 2,3-di (C1-C5 alkyl) -1, 3-butadienes are suitable in particular. 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, aryl-1, 3-butadiene, 1, 3-pentadiene, 2,4-hexadiene. Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tertiobutylstyrene, methoxystyrenes, ch I orostyrenes, vinyl mesitylene, divinylbenzene. , vinylnaphthalene.

The copolymers can contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinyl aromatic units. The elastomers can have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent used. The elastomers can be, for example, block, statistical, sequenced, microsequenced, and be prepared in dispersion or in solution; they can be coupled and / or starred or even functionalized with a coupling and / or star-forming or functionalizing agent. The term “function” here preferably means an interactive chemical group with the reinforcing filler of the composition.

Preferably, the elastomer of the composition mainly comprises an essentially unsaturated diene elastomer. The elastomer of the composition is preferably chosen from the group consisting of polybutadienes (abbreviated "BR"), synthetic (IR) or natural (NR) polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers. Such butadiene and isoprene copolymers are more preferably, respectively, butadiene-styrene copolymers (SBR) and isoprene-styrene copolymers (SIR).

More preferably, the majority elastomer is chosen from the group consisting of polybutadienes (BR), butadiene-styrene copolymers (SBR), natural polyisoprenes (NR) or synthetic (IR) and mixtures of these elastomers.

1-2 Strengthening charge

The composition according to the invention comprises a reinforcing filler. Any type of reinforcing filler known for its capacity to reinforce a rubber composition which can be used for the manufacture of tires can be used, for example an organic filler such as carbon black, an inorganic reinforcing filler such as silica, alumina, or a blend of these two types of filler. Preferably, the rate of reinforcing filler is in a range from 5 to 200 phr, preferably from 20 to 160 phr.

For the purposes of the invention, the reinforcing filler is preferably chosen from the group consisting of silicas, carbon blacks and mixtures of these. More preferably, the reinforcing filler is mainly carbon black, preferably at a rate comprised in a range ranging from 30 to 90 phr. Also preferably, the reinforcing filler is mainly silica, preferably at a rate comprised in a range ranging from 30 to 90 phr.

As carbon blacks, all the carbon blacks, in particular the so-called pneumatic blacks, are suitable. Among the latter, there may be mentioned more particularly the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as for example the blacks N 1 15, N134, N234, N326, N330, N339, N347, N375, or , depending on the intended applications, the blacks of higher series (for example N660, N683, N772). The carbon blacks could for example already be incorporated into an isoprene elastomer in the form of a masterbatch (see for example applications WO 97/36724 or WO 99/16600).

As examples of organic fillers other than carbon blacks, mention may be made of organic fillers of functionalized polyvinyl as described in applications WO-A-2006/069792, WO-A-2006/069793, WO-A- 2008/003434 and WO-A-2008/003435.

The composition may contain a type of silica or a blend of several silicas. The silica used can be any reinforcing silica known to a person skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface as well as a CTAB specific surface both of which are less than 450 m2 / g, preferably from 30 to 400 m2 / g. As highly dispersible precipitated silicas (known as "HDS"), mention will be made, for example, of "Ultrasil 7000" and "Ultrasil 7005" from Evonik, "Zeosil" 1165MP, 1135MP and 11 15MP from Solvay, “Hi-Sil EZ150G” silica from the company PPG, “Zeopol” silicas 8715, 8745 and 8755 from the Huber company, treated precipitated silicas such as for example the “doped” silicas with aluminum described in the EP application -A-0735088 or silicas with a high specific surface as described in application WO 03/16387. The silica preferably has a BET surface of between 45 and 400 m2 / g, more preferably between 60 and 300 m2 / g. These compositions can optionally also contain, in addition to the coupling agents, coupling activators, agents for recovery of inorganic charges or more generally agents for aid in the use which are capable in known manner, thanks to a improving the dispersion of the filler in the rubber matrix and lowering the viscosity of the compositions, improving their ability to be used in the raw state, these agents being, for example, hydrolysable silanes such as alkylalkoxysilanes, polyols, fatty acids, polyethers, primary, secondary or tertiary amines, hydroxylated or hydrolyzable polyorganosiloxanes.

Those skilled in the art will understand that as an equivalent filler of the silica described in this paragraph, a reinforcing filler of another nature, in particular organic, could be used, as soon as this reinforcing filler is covered with a silica layer, or else would have on its surface functional sites, in particular hydroxylated, requiring the use of a coupling agent to establish the connection between the filler and the elastomer.

The physical state in which the reinforcing filler is present is immaterial, whether in the form of powder, microbeads, granules, beads or any other suitable densified form.

1-3 Crosslinking system

In the composition of the invention, any type of crosslinking system known to those skilled in the art can be used for rubber compositions.

Preferably, the crosslinking system is a vulcanization system, that is to say based on sulfur (or a sulfur donor agent) and a primary vulcanization accelerator. To this basic vulcanization system can be added, incorporated during the first non-productive phase and / or during the productive phase as described later, various secondary accelerators or known vulcanization activators such as oxide zinc, stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine).

Sulfur is used at a preferential rate between 0.5 and 10 phr, more preferably between 0.5 and 5 phr, in particular between 0.5 and 3 phr. The vulcanization system of the composition according to the invention may also comprise one or more additional accelerators, for example the compounds of the thiuram family, zinc dithiocarbamate derivatives, sulfenamides, guanidines or thiophosphates. Any compound capable of acting as an accelerator for the vulcanization of diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type and their derivatives, accelerators of the thiuram type, zinc dithiocarbamates, can be used in particular. These accelerators are more preferably chosen from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyle sulfenamide (abbreviated "CBS"), N, N-dicyclohexyl-2-benzothiazyle sulfenamide (abbreviated "DCBS"), N-tert-butyl-2-benzothiazyle sulfenamide (abbreviated "TBBS"), N-tert-butyl-2-benzothiazyl sulfenimide (abbreviated "TBSI"), zinc dibenzyldithiocarbamate (en abbreviated "ZBEC") and mixtures of these compounds. Preferably, a primary accelerator of the sulfenamide type is used.

1-4 Rubber crumb

The composition of the invention also comprises from 5 to 100 phr of a rubber crumb (abbreviated as "crumb" in the following).

The crumbs are in the form of granules, optionally put in the form of a rubber plate. Most often, the rubber crumbs come from the grinding or micronization of cooked rubber compositions already used for a first application, for example in tires, they are a product for recycling materials. The powders therefore preferably consist of a composition based on at least one elastomer and a filler. Preferably the powders are in the form of microparticles.

By “microparticles” is meant particles which have a size, namely their diameter in the case of spherical particles or their largest dimension in the case of anisometric particles, of a few tens or hundreds of microns.

For the purposes of the invention, the rubber crumb has an average size D50 of between 100 and 300 μm, and a particle size distribution such that the ratio of the average sizes D10 / D50 is greater than or equal to 0 , 5, preferably between 0.55 and 0.95 and more preferably between 0.6 and 0.9, and more preferably still between 0.65 and 0.85. These specific powders can be obtained by different technologies, in particular by cryogenic micronization processes as described in documents US 7,445,170 and US 7,861, 958. According to another embodiment of the invention, the powders can be obtained by other micronization methods known to those skilled in the art and not limited to the cryogenic method alone.

Depending on the size distribution of objects obtained, the crumb obtained by the aforementioned processes can undergo an additional sieving step so as to control this distribution. The sieving can be carried out by various technologies (vibration, centrifugation, aspiration) known to those skilled in the art.

Also, commercially available crumbs such as the "PD80" crumb from the company Lehigh Technologies can be used.

Preferably, the crumb is present at a rate comprised in a range ranging from 5% to 40% by mass, preferably from 10% to 30% and more preferably from 15 to 25%. In a typical composition intended for tires, these mass rates correspond to rates of 5 to 100 phr. Below 5 pce the savings made would not be significant enough; while above 100 phr, the cohesion properties of the composition may be penalized. Thus, the level of crumb is preferably within a range ranging from 10 to 90 phr, preferably from 15 to 90 phr, more preferentially from 20 to 80 phr, and very preferentially from 30 to 70 phr for optimum operation of the invention.

As previously discussed, the powders preferably consist of a composition based on an elastomer and a filler. They can also include all the ingredients usually used in rubber compositions such as plasticizers, antioxidants, vulcanization additives, etc.

Thus, the powder includes an elastomer, preferably a diene elastomer. This elastomer preferably represents at least 30% by mass, more preferably at least 35% by mass, even more preferably at least 45% by mass of the weight of the crumb, percentage determined according to standard ASTM E1131. It is preferably chosen from the group consisting of polybutadienes, polyisoprenes including natural rubber, butadiene copolymers and isoprene copolymers. More preferably, the molar level of units of diene origin (conjugated dienes) present in the diene elastomer is greater than 50%, preferably between 50% and 70%. According to a preferred embodiment of the invention, the crumb contains between 5 and 80% by mass of filler, more preferably between 10% and 75%, and very preferably between 15% and 70%.

By filler is meant here any type of filler, whether it is reinforcing (typically with nanometric particles, and preferably of average size by weight less than 500 nm, in particular between 20 and 200 nm) or that it is not - reinforcing or inert (typically with micrometric particles, and preferably of average size by weight greater than 1 μm, for example between 2 and 200 μm). The average size by weight of the nanometric particles is measured in a manner well known to a person skilled in the art (by way of example, according to application WO2009 / 083160 paragraph 1.1). The average size by weight of the micrometric particles can be determined by mechanical sieving.

Examples of fillers known to be reinforcing by a person skilled in the art, there may be mentioned in particular carbon black or an inorganic reinforcing filler such as silica or alumina in the presence of a coupling agent, or their mixtures.

According to a preferred embodiment of the invention, the crumb comprises as a filler a reinforcing filler, in particular a carbon black or a mixture of carbon blacks.

The carbon black or the mixture of carbon blacks preferably represents more than 50%, more preferably more than 80%, even more preferably more than 90% by mass of the weight of the reinforcing filler of the crumb. According to a more preferred embodiment, the reinforcing filler consists of a carbon black or a mixture of carbon blacks.

Very preferably, the carbon black is present in the crumb at a rate ranging from 20 to 40% by mass, more preferably from 25 to 35% by mass.

As carbon blacks, all carbon blacks are suitable, in particular blacks of the HAF, ISAF, SAF, FF, FEF, GPF and SRF type conventionally used in rubber compositions for tires (so-called pneumatic grade blacks).

The crumb can contain all the other usual additives which enter into a rubber composition, in particular for tires. Among these usual additives, mention may be made of liquid or solid plasticizers, non-reinforcing fillers such as chalk, kaolin, protective agents, vulcanizing agents. These additives may also be found in the crumb in the form of a residue or derivative, since they may have reacted during the stages of manufacture of the composition or of crosslinking of the composition from which the crumb originated.

Regarding the constituents of the crumb, it is preferred for the needs of the invention that the crumb has an acetone extract of between 3 and 30% by mass, more preferably included in a range from 5 to 25% by mass.

Also, it is preferable that the crumb has a chloroform extract of between 5 and 85% by mass, more preferably included in a range ranging from 5 to 50% by mass.

The crumbs can be simple shredded / micronized rubber, without further treatment. It is also known that these powders can undergo a treatment in order to modify them. This treatment can consist of a chemical modification of functionalization or devulcanization. It can also be a thermomechanical, thermochemical, biological treatment ...

It is possible for the invention, to use a crumb which has a morphology modified by thermal and / or mechanical, and / or biological and / or chemical treatment. This type of crumb has an acetone extract of between 5 and 20% by mass, more preferably included in a range ranging from 10 to 18% by mass. Also, these crumbs have a chloroform extract of between 15 and 85% by mass, more preferably included in a range ranging from 15 to 50% by mass. Preferably, the chloroformic extract of such a rubber crumb has a mass-average molecular mass (Mw) greater than 10,000 g / mol, preferably greater than 20,000 g / mol and more preferably greater than 30,000 g / mol. This type of crumb is such that the ratio of the chloroform extract to the acetone extract, expressed in percentage by mass, is greater than or equal to 1.5; preferably greater than 2.

Preferably for the invention, a crumb is used which has not undergone any modification by heat and / or mechanical treatment, and / or biological and / or chemical treatment. Preferably, this type of powder has an acetone extract of between 3 and 15% by mass, more preferably included in a range ranging from 3 to 10% by mass. Also, it is preferred that the powder has a chloroform extract of between 3 and 20% by mass, more preferably included in a range ranging from 5 to 15% by mass. Preferably, the extract chloroform of rubber crumb has a weight average molecular weight (Mw) of less than 10,000 g / mol, preferably less than 8,000 g / mol. Preferably in this type of crumb, the ratio of the chloroform extract to the acetone extract, expressed in percentage by mass, is less than 1.5.

1-5 Specific hydrocarbon resin - tackifying resin

The composition according to the invention comprises a specific hydrocarbon resin, called tackifying resin. This tackifying resin has a number average molecular mass (Mn) greater than 800 g / mol and a polymolecularity index (Ip) greater than or equal to 2.0. The number average molecular mass (Mn) and the polymolecularity index (Ip) are measured by the size exclusion chromatography (SEC) technique, according to the methods defined below.

For the purposes of the invention, this tackifying resin is present at a rate ranging from 1 to 10 phr, preferably from 1 to 8 phr, more preferably from 2 to 7 phr. Below 1 phr, the effect of the resin is not sufficient, while beyond 10 phr the resin could modify the stiffness and glass transition temperature properties of the composition.

Preferably, the tackifying resin has a glass transition temperature, Tg, comprised in a range from -50 ° C. to 100 ° C., more preferably from 40 to 60 ° C. The Tg is measured according to ASTM D3418 (1999).

Preferably, the tackifying resin has a softening point in a range from 0 to 160 ° C, preferably from 90 to 110 ° C. The softening point is measured according to ISO 4625 ("Ring and Bail" method).

Preferably, the tackifying resin has an Mn greater than 1000 g / mol, more preferably greater than 1200 g / mol.

Preferably, the tackifying resin has an Ip greater than 2.0, more preferably greater than 2.1.

The tackifying resin useful for the needs of the invention can be chosen from natural or synthetic resins. Among the synthetic resins, it can preferably be chosen from aliphatic or aromatic thermoplastic hydrocarbon resins or else of the aliphatic / aromatic type, that is to say based on aliphatic and / or aromatic monomers. As monomers aromatics are suitable, for example, styrene, alpha-methylstyrene, ortho-, meta-, para-methylstyrene, vinyl-toluene, para-tertiobutylstyrene, methoxystyrenes, ch I orostyrenes, vinyl mesitylene, divinylbenzene, vinylnaphthalene, any vinyl aromatic monomer resulting from a C9 cut (or more generally from a C8 to C10 cut). Preferably, the vinyl aromatic monomer is styrene or a vinyl aromatic monomer derived from a C9 cut (or more generally from a C8 to C10 cut). Preferably, the vinyl aromatic monomer is the minority monomer, expressed in molar fraction, in the copolymer considered.

According to a particularly preferred embodiment, the tackifying resin useful for the needs of the invention is chosen from the group consisting of aliphatic hydrocarbon resins and mixtures of the latter and in particular from homopolymer resins or cyclopentadiene copolymers (abbreviated as CPD) or dicyclopentadiene (abbreviated as DCPD), homopolymer resins or C5 cut copolymers and mixtures thereof.

1-6 Other possible additives

The rubber compositions in accordance with the invention optionally also include all or part of the usual additives usually used in elastomer compositions intended in particular for the manufacture of treads, such as for example pigments, protective agents such as as anti-ozone waxes, anti-ozone chemicals, antioxidants, plasticizing agents (such as oils or plasticizing resins, different from the tackifying resins previously described), anti-fatigue agents, reinforcing resins, acceptors (for example example novolak phenolic resin) or methylene donors (for example HMT or H3M).

Of course, the compositions according to the invention can be used alone or in blends (i.e., mixed) with any other rubber composition which can be used for the manufacture of tires.

It goes without saying that the invention relates to the rubber compositions described above both in the so-called "raw" or non-crosslinked state (ie, before baking) and in the so-called "cooked" or crosslinked state, or still vulcanized (ie, after crosslinking or vulcanization). II- Preparation of the rubber compositions

The compositions are produced in suitable mixers, using two successive preparation phases well known to those skilled in the art: a first working phase or thermo-mechanical kneading (sometimes called the "non-productive" phase) at high temperature, up to a maximum temperature between 1 10 ° C and 200 ° C, preferably between 130 ° C and 180 ° C, followed by a second phase of mechanical work (sometimes referred to as the "productive" phase) at lower temperature, typically less than 110 ° C, for example between 60 ° C and 100 ° C, finishing phase during which the crosslinking or vulcanization system is incorporated; such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301.

The first phase (non-productive) is preferably carried out in several thermomechanical stages. During a first step, elastomers, reinforcing fillers, crumb (and optionally tackifying resin, coupling agents and / or other ingredients) are introduced into a suitable mixer such as a conventional internal mixer. with the exception of the crosslinking system), at a temperature between 20 ° C and 100 ° C and, preferably, between 25 ° C and 100 ° C. After a few minutes, preferably from 0.5 to 2 min and a rise in temperature to 90 ° C to 100 ° C, the other ingredients (that is to say, those which remain if all have not been put at the start) are added all at once or in parts, with the exception of the crosslinking system during mixing ranging from 20 seconds to a few minutes. The total duration of the kneading, in this non-productive phase, is preferably between 2 and 10 minutes at a temperature less than or equal to 180 ° C., and preferably less than or equal to 170 ° C.

After cooling the mixture thus obtained, the crosslinking system is then incorporated at low temperature (typically less than 100 ° C), generally in an external mixer such as a cylinder mixer; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for characterization in the laboratory, or else extruded, to form for example a rubber profile used for manufacturing semi-finished products for tires. These products can then be used for the manufacture of tires, according to known techniques skilled in the art, with the advantage of the invention, namely a good tacky layers on each other before curing the tire.

The crosslinking (or baking) is carried out in a known manner at a temperature generally between 130 ° C and 200 ° C, under pressure, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the baking temperature, of the crosslinking system adopted, of the crosslinking kinetics of the composition under consideration or of the size of the tire.

The following examples illustrate the invention without, however, limiting it.

III- Examples of embodiment of the invention

111-1 Characterization of the crumbs and rubber compositions of the examples

In the examples, the rubber crumbs are characterized as indicated below.

Measuring the size of the powder particles:

The size distribution by mass of the powder particles can be measured by laser particle size, on an apparatus of the mastersizer 3000 type from the company Malverne. The measurement is carried out in a liquid way, diluted in alcohol after a preliminary treatment of 1 min of ultrasound in order to guarantee the dispersion of the particles. The measurement is carried out in accordance with ISO-13320-1 and makes it possible to determine in particular the D10 and the D50, that is to say the average diameter below which respectively 10% by mass and 50% by mass of the population total of particles is present.

Measurement of the mass fraction of carbon black:

The measurement of the mass fraction of carbon black is made by a thermogravimetric analysis (ATG) according to standard NF T-46-07, on an apparatus of the company Mettler Toledo model "TGA / DSC1". About 20g of sample is introduced into the thermal analyzer, then subjected to a thermal program from 25 to 600 ° C under an inert atmosphere (pyrolyzable phase) then from 400 to 750 ° C under an oxidizing atmosphere (oxidizable phase). The mass of the sample is measured continuously throughout the thermal program. The rate of organic matter corresponds to the loss of mass measured during the pyrolyzable phase compared to the mass of the sample initial. The black content corresponds to the loss of mass measured during the oxidizable phase compared to the initial sample mass.

Measurement of the acetone extract:

The acetone extract rate is measured according to ISO1407, using a soxhlet type extractor.

A sample test portion (between 500 mg and 5 g) is introduced into an extraction cartridge and then placed in the extractor tube of the soxhlet. A volume of acetone equal to two or three times the volume of the extractor tube is placed in the collector of the soxhlet. The soxhlet is then assembled and then heated for 16 hours.

The sample is weighed after extraction. The level of acetone extract corresponds to the loss of mass of the sample during the extraction, compared to its initial mass.

One can also calculate the rate of elastomer, which corresponds to the rate of organic matter determined by thermogravimetric analysis from which the rate of acetone extract is subtracted.

Measurement of chloroform extract:

The chloroform extract rate is measured according to ISO1407, using a soxhlet extractor.

A sample test portion (between 500 mg and 5 g) is introduced into an extraction cartridge and then placed in the extractor tube of the soxhlet. A volume of chloroform equal to two or three times the volume of the extractor tube is placed in the collector of the soxhlet. The soxhlet is then assembled and then heated for 16 hours.

The sample is weighed after extraction. The level of chloroform extract corresponds to the loss of mass of the sample during the extraction, compared to its initial mass.

Measurement of the average molecular weights of the chloroform extract:

The molecular weights are determined by size exclusion chromatography, according to a Moore calibration and according to ISO16014.

The weight average molecular weight (Mw) of the chloroform extract is measured by steric exclusion chromatography (SEC) with a refractive index (RI) detector. The system consists of an Alliance 2695 chain from Waters, a column oven from Waters and an RI 410 detector from Waters. The column set used is composed of 2 PL GEL columns MIXED D (300 x 7.5 mm 5pm) followed by 2 columns PL GEL MIXED E (300 x 7.5 mm 3pm) from the company Agilent. These columns are placed in a column oven thermostatically controlled at 35 ° C. The mobile phase used is non-antioxidant tetrahydrofuran. The flow rate of the mobile phase is 1 ml / min. The RI detector is also thermostatically controlled at 35 ° C.

The chloroform extract is dried under a stream of nitrogen. The dry extract is then taken up at 1 g / l in non-antioxidized tetrahydrofuran at 250 ppm for 2 hours with stirring. The solution obtained is filtered using a syringe and a 0.45pm syringe filter in disposable PTFE. 100 ml of the filtered solution is injected into the chromatographic system conditioned at 1 ml / min and 35 ° C.

The Mw results are provided by integration of the chromatographic peaks detected by an RI detector beyond a value of 2000 g / mol. The Mw is calculated from a calibration carried out using standard polystyrenes.

In the examples, the rubber compositions are characterized before curing as indicated below.

Raw tights (or tack):

Tack is the ability of an assembly of unvulcanized mixtures to resist tearing stress.

Is used for the measurement of raw tack (tack) a test device is inspired by the probe tack tester (ASTM D2979-95). An Instron traction machine is used comprising a fixed metal jaw and a movable metal jaw. A first test piece made of a 3mm thick mixing film is bonded to the fixed jaw. A second test piece made of a 3mm thick mixing film is bonded to the movable jaw. The mixing films are bonded to the surface of the metal jaws with a double-sided adhesive (Tesafix® 4970).

For the preparation of the mixing test pieces, the mixing films are obtained by calendering to a thickness of 3 mm. The test pieces are cut using a 1 cm diameter cookie cutter.

The principle of the measurement consists in bringing the two mixing films into contact for 16 seconds by applying a compression force of 30 N. After this contact phase, they are separated by driving the cross member of the traction machine . The speed of movement of the crosspiece in this tearing phase is 60mm / s. The displacement of the cross member and the force are measured continuously as a function of time during the contact and tear-off phases.

The raw pantyhose result is the measurement of the maximum force (in Newton, N) reached during the tearing off. A value of 35 N and more is considered to be a good performance in the context of the present invention. ..

Percentage of recycled material in the mixture:

The percentage of recycled material in the mixture is determined by taking into account the mass rate of rubber crumb relative to the total weight of the mixture comprising the rubber crumb and the other ingredients of the composition. This percentage is 0% in the reference mixture not comprising a rubber crumb, and it is calculated as indicated above for each mixture comprising a crumb.

111-2 Preparation of the crumbs

For the preparation of these crumbs, any composition may be suitable. For the exemplary embodiments, the crumbs used come from the recycling of HGV tires.

The crumbs used in the examples of compositions below were prepared by cryogenic grinding according to the process described in document US 7,445,170, comprising the successive and independent stages of granulation, separation of metallic and textile reinforcements, cooling and micronization in order to obtain a gross distribution of micron particles of vulcanized mixture. This micronization is carried out using a conical impact crusher as described in document US 7,861, 958. The cryogenic input enters the mill, then is transferred by gravity to a rotor rotating at high speed. The cryogenic input is thus projected onto the walls of the rotor chamber on multiple occasions leading to its micronization. The particles then pass through a series of two vibrating screens of the same size (20 mesh) in order to separate the last elements not made up of vulcanized mixture. A crude distribution of micron particles of vulcanized mixture is obtained.

An additional separation step according to a size criterion was carried out to obtain the other crumbs used in composition in the exemplary embodiments. This separation step is carried out using a series of sieves stacked in order of size. Thus, the largest particles are retained on the sieve while the smallest pass to the lower stage on the next sieve. Those skilled in the art will understand that the distributions considered below can be composed of all of the particles passing a given sieve or of all of the particles retained between 2 stages.

The size distribution not retained by a 40mesh sieve constitutes the "crumb 1" mentioned below.

The size distribution not retained by a 60mesh sieve constitutes the "crumb 2" mentioned below.

The size distribution between a 80mesh sieve and a 140mesh sieve constitutes the "crumb 3" mentioned below.

The size distributions of the 3 powders considered in the composition examples, determined by laser particle size, are shown in Table 1 below. This table also presents the composition characteristics of these powders.

Table 1

111-3 Rubber compositions

The compositions are produced with an introduction of all of the constituents on an internal mixer, with the exception of the vulcanization system. The vulcanizing agents (sulfur and accelerator) are introduced on an external mixer at low temperature (the cylinders constituting the mixer being at around 30 ° C).

The examples presented in Table 2 are intended to compare the different rubber properties of compositions according to the invention (C6 to C9) with the properties of compositions not in accordance with the invention (C0 to C5). The properties are presented in Table 3.

Table 2

(1) NR: Natural rubber

(2) BR: polybutadiene "CB24" from the company Lanxess; 96% 1,4-cis; Tg = -107 ° C

(3) SBR with 26.5% by weight of styrene unit and 24% of unit 1, 2 of the butadiene part (Tg = - 48 ° C)

(4) Carbon black Grade ASTM N375

(5) Crumbs 1 to 3 as presented in table 1

(6) MES Oil (Medium Extracted Solvates) ("Catenex SNR" from Shell)

(7) Tackifying resin "Escorez 1,102" from the company EXXON (Mn 1370 g / mol; lp = 2.3)

(8) N- (1, 3-dimethylbutyl) -N’-phenyl-p-phenylenediamine (Santoflex 6-PPD) from the company Flexsys

(9) Stearin “Pristerene 4931” from the company Uniqema

(10) Industrial grade zinc oxide - Umicore company

(1 1) N-cyclohexyl-2-benzothiazol-sulfenamide ("Santocure CBS" from the company Flexsys) Table 3

It is noted that the compositions comprising a crumb make it possible to integrate into the mixture a large amount of recycled material from 21 to 22% approximately, and therefore to reduce the environmental impact. However, it is also noted for the compositions not in accordance with the invention that the performance of raw tights (CAC) is lowered below 35N, including by adding a tackifying resin. On the other hand, the specific crumb of the invention allows a good sticky raw, even without tackifying resin, and in the presence of such a resin, makes it possible to reach a level as efficient as the control, while presenting a higher rate recycled material (and therefore a lower environmental impact).

Claims

1. A rubber composition based on at least one elastomer, a reinforcing filler, a crosslinking system and from 5 to 100 phr of a rubber crumb, said crumb having an average size D50 of between 100 and 300 μm, and a particle size distribution such that the ratio of mean sizes D10 / D50 is greater than or equal to 0.5; said composition further comprising 1 to 10 phr of a tackifying resin having a number average molecular mass (Mn) greater than 800 g / mol and a polymolecularity index (Ip) greater than or equal to 2.0.

2. Composition according to claim 1 wherein the rubber crumb has a ratio of average sizes D10 / D50 of between 0.55 and 0.95 and more preferably between 0.6 and 0.9.

3. Composition according to any one of the preceding claims, in which the rubber crumb is present at a rate ranging from 10 to 90 phr.

4. Composition according to any one of the preceding claims, in which the rubber crumb has an acetone extract of between 3 and

30% by mass, more preferably included in a range from 5 to 25% by mass.

5. Composition according to any one of the preceding claims, in which the rubber crumb has a chloroform extract of between 5 and 85% by mass, more preferably included in a range ranging from 5 to 50% by mass.

6. Composition according to any one of claims 1 to 3 in which the rubber crumb has not been modified by heat and / or mechanical, and / or biological and / or chemical treatment.

7. Composition according to Claim 6, in which the rubber crumb has an acetone extract of between 3 and 15% by mass, more preferably included in a range ranging from 3 to 10% by mass.

8. Composition according to any one of claims 6 or 7 in which the rubber crumb has a chloroformic extract of between 3 and 20% mass, more preferably included in a range from 5 to 15% by mass.

9. Composition according to any one of claims 6 to 8 in which the rubber crumb has a ratio of the chloroformic extract to the acetonic extract, expressed in percentage by mass, of less than 1.5.

10. Composition according to any one of claims 6 to 9 in which the rubber crumb has a chloroformic extract whose weight average molecular mass is less than 10,000 g / mol, preferably less than 8000 g / mol.

1 1. Composition according to any one of the preceding claims, in which the rubber crumb has a mass fraction of carbon black ranging from 20 to 40%, preferably ranging from 25 to 35%.

12. Composition according to any one of the preceding claims, in which the elastomer mainly comprises an elastomer chosen from the group consisting of essentially unsaturated diene elastomers.

13. Composition according to the preceding claim in which the majority elastomer is chosen from the group consisting of polybutadienes, polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

14. Composition according to the preceding claim in which the majority elastomer is chosen from the group consisting of polybutadienes, butadiene-styrene copolymers, natural or synthetic polyisoprenes and mixtures of these elastomers.

15. Composition according to any one of the preceding claims, in which the reinforcing filler is chosen from the group consisting of silicas, carbon blacks and mixtures of the latter.

16. Composition according to any one of the preceding claims, in which the rate of reinforcing filler is within a range ranging from 5 to 200 phr, preferably from 20 to 160 phr.

17. Composition according to any one of the preceding claims, in which the majority reinforcing filler is carbon black, preferably at a rate ranging from 30 to 90 phr.

18. Composition according to any one of claims 1 to 16 in which the majority reinforcing filler is silica, preferably at a rate included in a range ranging from 30 to 90 phr.

19. Composition according to any one of the preceding claims, in which the rate of tackifying resin is within a range ranging from 1 to 8 phr, preferably from 2 to 7 phr.

20. Composition according to any one of the preceding claims, in which the tackifying resin has a number average molecular mass (Mn) greater than 1000 g / mol, preferably greater than 1200 g / mol.

21. Composition according to any one of the preceding claims, in which the tackifying resin has a polymolecularity index (Ip) greater than 2.0, preferably greater than 2.1.

22. A tire comprising a composition according to any one of claims 1 to 21.

23. A tire according to the preceding claim comprising a composition according to any one of claims 1 to 21 in all or part of its tread.