EP4232302A1

EP4232302A1 - A rubber composition

Info

Publication number: EP4232302A1
Application number: EP20804360.4A
Authority: EP
Inventors: Yasufumi NAKASHIMA
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2020-10-22
Filing date: 2020-10-22
Publication date: 2023-08-30
Also published as: CN116472312A; WO2022085165A1

Abstract

A rubber composition is based on at least an elastomer matrix, a reinforcing filler, a reinforcing resin, more than 0 phr and less than 5 phr of an anti-ozone wax, and a crosslinking system based on zinc oxide and stearic acid in amounts such that a ratio of the amount, in phr, of zinc oxide and of stearic acid is more than 3.

Description

A RUBBER COMPOSITION

The field of the invention is that of a rubber composition intended in particular for a rubber article, in more particular for a tire.

It is known to use, in some parts of rubber articles, rubber composition exhibiting a high stiffness during small strain of the rubber strains. Resistance to small strains is one of the mechanical properties which the rubber articles have to exhibit in order to respond to stress to which it is subjected.

WO2015/189804

The patent literature 1 discloses that reinforcing fillers and reinforcing resins are incorporated in constituent rubber compositions of parts of rubber articles in order to obtain the mechanical properties.

A constant objective of rubber article manufacturers is to add another useful function in such rubber compositions while maintaining reasonable level on the mechanical properties.

During the research, the inventor has discovered that a specific rubber composition intended in particular for a rubber article, which allows an unexpectedly improved the ozone resistance of the rubber composition while maintaining reasonable levels on the stiffness and the hysteresis loss as the mechanical properties of the rubber composition.

In the present description, unless expressly stated otherwise, all the percentages (%) indicated are percentages by weight (wt%).

The expression “elastomer matrix” is understood to mean, in a given composition, all of the elastomers present in said rubber composition.

The abbreviation “phr” signifies parts by weight per hundred parts by weight of the elastomer matrix in the considered rubber composition.

In the present description, unless expressly indicated otherwise, each TgDSC (glass transition temperature) is measured in a known way by DSC (Differential Scanning Calorimetry) according to Standard ASTM D3418-08.

Any interval of values denoted by the expression “between a and b” represents the range of values of more than “a” and of less than “b” (i.e. the limits a and b excluded) whereas any interval of values denoted by the expression “from a to b” means the range of values going from “a” to “b” (i.e. including the strict limits a and b).

The expression “based on” should be understood in the present application to mean a composition comprising the mixture(s), the product of the reaction of the various constituents used or both, some of the constituents being able or intended to react together, at least partly, during the various manufacturing phases of the composition, in particular during the vulcanization (curing).

A first aspect of the invention is a rubber composition based on at least an elastomer matrix, a reinforcing filler, a reinforcing resin, more than 0 phr and less than 5 phr of an anti-ozone wax and a crosslinking system based on zinc oxide and stearic acid in amounts such that a ratio of the amount, in phr, of zinc oxide and of stearic acid is more than 3.

The specific rubber composition allows an unexpectedly improved the ozone resistance of the rubber composition while maintaining reasonable levels on the stiffness and the hysteresis loss as the mechanical properties of the rubber composition.

Each of the below aspect(s), the embodiment(s), the instantiation(s), and the variant(s) including each of the preferred range(s), matter(s) or both may be applied to any one of the other aspect(s), the other embodiment(s), the other instantiation(s) and the other variant(s) of the invention unless expressly stated otherwise.

The rubber composition according to the invention is based on an elastomer matrix.

Elastomer (or loosely “rubber”, the two terms being regarded as synonyms) of the “diene” type is to be understood in a known manner as an (meaning one or more) elastomer derived at least partly (i.e. a homopolymer or a copolymer) from diene monomers (monomers bearing two carbon-carbon double bonds, conjugated or not).

These diene elastomers can be classified into two categories: “essentially unsaturated” or “essentially saturated”. Generally, the expression “essentially unsaturated” is understood to mean a diene elastomer resulting at least in part from conjugated diene monomers having a content of units of diene origin (conjugated dienes) which is greater than 15% (mol %); thus it is that diene elastomers such as butyl rubbers or diene/α -olefin copolymers of the EPDM type do not fall under the preceding definition and may especially be described as “essentially saturated” diene elastomers (low or very low content of units of diene origin, always less than 15%). In the category of “essentially unsaturated” diene elastomers, the expression “highly unsaturated” diene elastomer is understood to mean in particular a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

Although it applies to any type of diene elastomer, a person skilled in the art of tires will understand that the invention is preferably employed with essentially unsaturated diene elastomers.

Given these definitions, the expression diene elastomer capable of being used in the compositions in accordance with the invention is understood in particular to mean:
(a) - any homopolymer obtained by polymerization of a conjugated diene monomer, preferably having from 4 to 12 carbon atoms;
(b) - any copolymer obtained by copolymerization of one or more conjugated dienes with one another or with one or more vinyl aromatic compounds preferably having from 8 to 20 carbon atoms.

The following are suitable in particular as conjugated dienes: 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di(C₁-C₅ alkyl)-1,3-butadienes, such as, for example, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1 ,3-butadiene or 2-methyl-3-isopropyl-1 ,3-butadiene, an aryl-1,3-butadiene, 1,3-pentadiene or 2,4-hexadiene. The following, for example, are suitable as vinylaromatic compounds: styrene, ortho-, meta- or para-methylstyrene, the“vinyltoluene” commercial mixture, para-(tert-butyl) styrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene or vinylnaphthalene.

A second aspect of the invention is the rubber composition according to the first aspect, wherein the elastomer matrix comprises at least one diene elastomer selected from the group consisting of a polyisoprene, a polybutadiene, a butadiene copolymer, an isoprene copolymer and combinations thereof.

According to a preferred embodiment of the above aspect, the polybutadiene has a content (molar %) of 1,2-units of between 4% and 80% or has a content (molar %) of cis-1,4-units of more than 80%, more preferably more than 90% (molar %), still more preferably at least 96% (molar %).

According to a preferred embodiment of the above aspect, the polyisoprene is natural rubber (NR), a synthetic polyisoprene (IR) or combinations thereof. The synthetic polyisoprene may be a synthetic cis-1,4-polyisoprene, preferably having a content (molar %) of cis-1,4 bonds of more than 90%, more preferably more than 95%, still more preferably more than 98%.

According to a preferred embodiment of the above aspect, the butadiene copolymer is selected from the group consisting of styrene butadiene copolymers (SBR), butadiene isoprene copolymers (BIR), styrene butadiene isoprene copolymers (SBIR) and combinations thereof.

According to a preferred embodiment of the above aspect, the isoprene copolymer is selected from the group consisting of butadiene isoprene copolymers (BIR), styrene isoprene copolymers (SIR), styrene butadiene isoprene copolymers (SBIR) and combinations thereof.

A third aspect of the invention is the rubber composition according to the first aspect or the second aspect, wherein the elastomer matrix comprises more than 50 phr, preferably more than 55 phr, more preferably more than 60 phr, still more preferably more than 65 phr, particularly more than 70 phr, more particularly more than 75 phr, still more particularly more than 80 phr, advantageously more than 85 phr, more advantageously more than 90 phr, still more advantageously more than 95 phr, especially 100 phr, of a polyisoprene.

According to a preferred embodiment of the second aspect or the third aspect, the polyisoprene comprises more than 50%, preferably more than 55%, more preferably more than 60%, still more preferably more than 65%, particularly more than 70%, more particularly more than 75%, still more particularly more than 80%, advantageously more than 85%, more advantageously more than 90%, still more advantageously 95%, especially 100%, by weight of natural rubber per 100% by weight of the polyisoprene.

The rubber composition according to the invention is based on a reinforcing filler.

Use may be made of any type of reinforcing filler known for its capabilities of reinforcing a rubber composition which can be used for the manufacture of the article, for example a reinforcing organic filler (such as carbon black), a reinforcing inorganic filler (such as silica, with which a coupling agent is combined in a known way) or combinations of the reinforcing organic filler and the reinforcing inorganic filler.

As carbon blacks, all carbon blacks conventionally used in tires (“tire-grade” blacks) are suitable, such as for example reinforcing carbon blacks of the 100, 200 or 300 series in ASTM grades (such as for example, the N115, N134, N234, N326, N330, N339, N347 or N375 blacks), or carbon blacks higher series, the 500, 600, 700 or 800 series in ASTM grades (such as for example the N550, N660, N683, N772, N774 blacks). The carbon blacks might for example be already incorporated in an elastomer matrix, for instance, a diene elastomer, in the form of a masterbatch.

A fourth aspect of the invention is the rubber composition according to any one of the first to the third aspects, wherein the amount of reinforcing filler is more than 20 phr, preferably more than 30 phr, more preferably more than 40 phr, still more preferably more than 50 phr, particularly more than 60 phr, more particularly more than 70 phr.

According to a preferred embodiment of the invention, the amount of reinforcing filler is less than 200 phr, preferably less than 150 phr, more preferably less than 120 phr, still more preferably less than 100 phr, particularly less than 90 phr, more particularly less than 80 phr.

A fifth aspect of the invention is the rubber composition according to any one of the first to the fourth aspects, wherein the reinforcing filler comprises more than 50%, preferably more than 55%, more preferably more than 60%, still more preferably more than 65%, particularly more than 70%, more particularly more than 75%, still more particularly more than 80%, advantageously more than 85%, more advantageously more than 90%, still more advantageously 95%, especially 100%, by weight of a carbon black per 100% by weight of the reinforcing filler.

According to a preferred embodiment of the fifth aspect, the carbon black is selected from the group consisting of 100 series, 200 series, 300 series and combinations thereof, preferably N115, N134, N234, N326, N330, N339, N347, N375 and combinations thereof, in ASTM.

The rubber composition according to the invention is based on a reinforcing resin.

A sixth aspect of the invention is the rubber composition according to any one of the first to the fifth aspects, wherein the amount of reinforcing resin is more than 1 phr, preferably more than 2 phr, more preferably more than 3 phr, still more preferably more than 4 phr, particularly more than 5 phr, more particularly more than 6 phr, still more particularly more than 7 phr, advantageously more than 8 phr, more advantageously more than 9 phr, still more advantageously more than 10 phr, especially more than 11 phr.

According to a preferred embodiment of the invention, the amount of reinforcing resin is less than 45 phr, preferably less than 42 phr, more preferably less than 39 phr, still more preferably less than 36 phr, particularly less than 33 phr, more particularly less than 30 phr, still more particularly less than 27 phr, advantageously less than 24 phr, more advantageously less than 21 phr, still more advantageously less than 18 phr, especially less than 15 phr.

The reinforcing resin (or curing resin) is known to a person skilled in the art for stiffening rubber compositions, in particular by increasing their Young's modulus or else the complex dynamic shear G*. Thus, a rubber composition to which a reinforcing resin has been added will exhibit a higher stiffness, in particular a Young's modulus or the complex dynamic shear G*, than this composition without reinforcing resin.

Those skilled in the art can measure the Young's modulus (also known as modulus of elasticity or else tensile modulus) of rubber compositions according to Standard ASTM 412-98a. or according to Standard NF EN ISO 527-2 (2012) on a test specimen of type A according to Standard DIN EN ISO 3167 (2014). They can also measure the complex dynamic shear G* on a viscosity analyzer (Metravib VA4000), in a way well known to a person skilled in the art according to Standard ASTM D 5992-96, for example by recording the response of a sample of crosslinked composition (cylindrical test specimen with a thickness of 4 mm and a cross section of 400 mm²), subjected to a simple alternating sinusoidal shear stress, at a frequency of 10 Hz, under the defined conditions of temperature (for example at 60℃) according to Standard ASTM D 1349-99 or, as the case may be, at a different temperature. A strain amplitude sweep is carried out from 0.1% to 50% (outward cycle) and then from 50% to 0.1% (return cycle). For the return cycle, the complex dynamic shear modulus G* at a predetermined strain (for example 10%) is shown.

In this context, the increase in the stiffness is brought about by polymerization or crosslinking of the reinforcing resin so as to form, in the vast majority of cases, a three-dimensional network. This crosslinking most of the time requires the use of a co-agent (often called a curing agent), of heating (at a temperature of greater than or equal to 100℃, indeed even of greater than or equal to 130℃) or combinations thereof.

The reinforcing resins conventionally used in rubber compositions for rubber articles are based on a methylene acceptor/donor system. The terms “methylene acceptor” and “methylene donor” are well known to a person skilled in the art and are widely used to denote compounds capable of reacting together (crosslinking). The crosslinking of the resin is brought about, during the curing of the rubber matrix, by the formation of methylene (-CH₂-) bridges between the carbons in the ortho, the para or both positions of the phenolic rings of the resin and the methylene donor, thus creating a three-dimensional resin network which is superimposed on and interpenetrated with the reinforcing filler/elastomer network, on the one hand, and with the elastomer/sulfur network, on the other hand (if the crosslinking agent is sulfur).

There are many other reinforcing resins which can be used in the context of the present invention, if appropriate combined with a co-agent of the reinforcing resin.

A seventh aspect of the invention is the rubber composition according to any one of the first to the sixth aspects, wherein the reinforcing resin is based on at least one reinforcing resin selected from the group consisting of a phenolic resin, an epoxy resin, a benzoxazine resin, a bismaleimide, a polyurethane resin and combinations thereof.

An eighth aspect of the invention is the rubber composition according to any one of the first to the seventh aspects, wherein the reinforcing resin is based on at least one phenolic resin selected from the group consisting of at least one resin based on polyphenol, alkylphenol, aralkylphenol and combinations thereof, preferably the reinforcing resin is at least one phenolic resin selected from the group consisting of at least one resin based on hydroxybenzene, bisphenol (particularly diphenylolpropane or diphenylolmethane), naphthol, cresol, t-butylphenol, octylphenol, nonylphenol, resorcinol, phloroglucinol, cardanol, xylenol (particularly 3,5-xylenol), 1-naphthol, 2-naphthol, 1,5-naphthalenediol, 2,7-naphthalenediol, pyrogallol, 2-methylhydroquinone, 4-methylcatechol, 2-methylcatechol, orcinol (5-methylbenzene- 1,3-diol), hydroquinone (benzene-1,4-diol) and combinations thereof.

According to a preferred embodiment of the invention, the reinforcing resin is based on at least one epoxy resin selected from the group consisting of an aromatic epoxy compound, alicyclic an epoxy compound, an aliphatic epoxy compound and combinations thereof, preferably, the reinforcing resin is based on at least one epoxy resin selected from the group consisting of 2,2-bis[4-(glycidyloxy)phenyl]propane, poly[(o-cresyl glycidyl ether)-co-formaldehyde], poly[(phenyl glycidyl ether)-co-formaldehyde], poly[(phenylglycidyl ether)-co-(hydroxybenzaldehyde glycidyl ether)] and combinations thereof.

A ninth aspect of the invention is the rubber composition according to any one of the first to the eighth aspects, wherein the rubber composition is further based on at least one co-agent of the reinforcing resin.

A tenth aspect of the invention is the rubber composition according to the ninth aspect, wherein the amount of co-agent of the reinforcing resin is more than 1 phr, preferably more than 2 phr, more preferably more than 3 phr, still more preferably more than 4 phr, particularly more than 5 phr, more particularly more than 6 phr.

According to a preferred embodiment of the ninth aspect or the tenth aspect, the amount of co-agent of the reinforcing resin is less than 20 phr, preferably less than 18 phr, more preferably less than 16 phr, still more preferably less than 14 phr, particularly less than 12 phr, more particularly less than 10 phr.

An eleventh aspect of the invention is the rubber composition according to the ninth aspect or the tenth aspect, wherein the co-agent of the reinforcing resin is based on at least one co-agent selected from the group consisting of a methylene donor, a polyaldehyde, a polyamine, a polyimine, a polyamine, a polyaldimine, a polyketimine, an acid anhydride and combinations thereof.

According to a preferred embodiment of any one of the ninth to the eleventh aspects, the reinforcing resin is based on at least one phenolic resin, and the co-agent of the reinforcing resin is based on at least one methylene donor selected from the group consisting of hexamethylenetetramine, hexa(methoxymethyl)melamine, hexa(ethoxymethyl)melamine, paraformaldehyde polymers, N-methylol derivatives of melamine, and combinations thereof, preferably selected from the group consisting of hexamethylenetetramine, hexa(methoxymethyl)melamine, hexa(ethoxymethyl)melamine and combinations thereof.

According to another preferred embodiment of any one of the ninth to the eleventh aspects, the reinforcing resin is based on at least one epoxy resin, and the co-agent of the reinforcing resin is based on at least one amino curing agent selected from the group consisting of polyamines (in particular aliphatic polyamines, alicyclic polyamines, aliphatic amines and aromatic polyamines), dicyandiamides, hydrazides, imidazole compounds, sulfonium salts, onium salts, ketimines, acid anhydrides and combinations thereof, preferably selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, 1,8-diaminooctane, 1,3-bis(aminomethyl)cyclohexane, which m-xylylenediamine, p-xylylenediamine, m-phenylenediamine, 2,2-bis(4-aminophenyl)propane, diaminodiphenylmethane, 3,5-diethyl-2,4-diaminotoluene, 3,5-diethyl-2,6-diaminotoluene, methyl thio-toluene diamine, dimethyl thio-toluene diamine, diaminodiphenyl sulfone, 2,2'-bis(4-aminophenyl)-p-diisopropylbenzene, 3,3’-diaminobenzidine, 4,4’-(4,4’-isopropylidenediphenoxy)bis(phthalic anhydride) polyanhydride, pyromellitic dianhydride and combinations thereof.

The reinforcing resins within the meaning of the present invention should not be confused with “plasticizing” hydrocarbon resins, which are by nature miscible (i.e. compatible) at the contents used with the polymer compositions for which they are intended, so as to act as true diluents. Plasticizing hydrocarbon resins have in particular been described, for example, in the work entitled "Hydrocarbon Resins" by R. Mildenberg, M. Zander and G. Collin (New York, V C H, 1997, ISBN 3-527-28617-9), Chapter 5 of which is devoted to the applications, in particular in the tire rubber field (5.5. “Rubber Tires and Mechanical Goods”). They can be aliphatic, cycloaliphatic, aromatic, hydrogenated aromatic or of the aliphatic/aromatic type.

The rubber composition according to the invention is based on more than 0 phr and less than 5 phr of an anti-ozone wax (or antiozonant wax).

According to preferred embodiment of the invention, the amount of anti-ozone wax is more than 0.5 phr.

According to preferred embodiment of the invention, the amount of anti-ozone wax is less than 4.5 phr, preferably less than 4 phr, more preferably less than 3.5 phr, still more preferably less than 3 phr, particularly less than 2.5 phr, more particularly less than 2 phr, still more particularly less than 1.5 phr, advantageously less than 1 phr.

According to a preferred embodiment of the invention, the anti-ozone wax is based on at least one film-forming anti-ozone wax, preferably the film-forming anti-ozone wax is selected from the group consisting of a paraffinic wax, a microcrystalline wax and combinations thereof. They consist of a mixture of linear alkanes and of non-linear alkanes (isoalkanes, cycloalkanes, branched alkanes) resulting from the refining of oil or from the catalytic hydrogenation of carbon monoxide (Fischer-Tropsch process) predominantly comprising chains of at least 20 carbon atoms.

According to a preferred embodiment of the invention, the anti-ozone wax is based on at least one natural wax, preferably the natural wax is selected from the group consisting of candelilla wax, carnauba wax and combinations thereof.

Mention may be made of the commercial waxes Varazon 4959 or Varazon 6500 or also Varazon 6810 from Sasol, Ozoace 0355 from Nippon Seiro, Negozone 9343 from H&R and H3841 from Yanggu Huatai.

A twelfth aspect of the invention is the rubber composition according to any one of the first to the eleventh aspects, wherein the anti-ozone wax is based on from 50% to 75% of linear alkanes based on from 30 carbon atoms to 38 carbon atoms, with respect to the total amount of linear alkanes.

The rubber composition according to the invention is based on a crosslinking system based on zinc oxide and stearic acid in amounts such that a ratio of the amount, in phr, of zinc oxide and of stearic acid is more than 3, preferably more than 4, more preferably more than 5, still more preferably more than 6, particularly more than 7, more particularly more than 8, still more particularly more than 9, in order to avoid anti-reversion that deteriorates the mechanical properties of the rubber composition.

According to a preferred embodiment of the invention, the ratio of the amount, in phr, of zinc oxide and of stearic acid is less than 16, preferably less than 15, more preferably less than 14, still more preferably less than 13, particularly less than 12, more particularly less than 11, still more particularly less than 10.

A thirteenth aspect of the invention is the rubber composition according to any one of the first to the twelfth aspects, wherein the amount of zinc oxide is more than 3 phr, preferably more than 4 phr, more preferably more than 5 phr, still more preferably more than 6 phr, particularly more than 7 phr.

According to a preferred embodiment of the invention, the amount of zinc oxide is less than 12 phr, preferably less than 11 phr, more preferably less than 10 phr, still more preferably less than 9 phr, particularly less than 8 phr.

A fourteenth aspect of the invention is the rubber composition according to any one of the first to the thirteenth aspect, wherein the amount of stearic acid is less than 3 phr, preferably less than 2 phr, more preferably less than 1 phr.

According to a preferred embodiment of the invention, the amount of stearic acid is more than 0 phr.

The crosslinking system can be based on, other than zinc oxide and stearic acid, sulfur (sulphur), a donor of sulfur, peroxide, a bismaleimide, a vulcanization accelerator, a vulcanization activator (for example, a guanidine derivative (in particular diphenylguanidine)), a vulcanization retarder (for example, N-cyclohexylthiophthalimide), an anti-reversion agents (for example, hexamethylene thiosulfate salt) or combinations thereof.

According to a preferred embodiment of the invention, the crosslinking system is based on sulfur, preferably the amount of sulfur is more than 1 phr, more preferably more than 2 phr, still more preferably more than 3 phr, particularly more than 4 phr, more particularly more than 5 phr, still more particularly more than 6 phr.

According to a preferred embodiment of the invention, the crosslinking system is based on sulfur, preferably the amount of sulfur is less than 12 phr, more preferably less than 11 phr, still more preferably less than 10 phr, particularly less than 9 phr, more particularly less than 8 phr, still more particularly less than 7 phr.

The amount in phr of sulfur is to say the amount of vulcanization sulfur content in phr. The vulcanization sulfur may be sulfur, sulfur derived from a sulfur-donating agent or combinations thereof.

According to a preferred embodiment of the invention, the crosslinking system is based on at least one vulcanization accelerator, preferably the amount of vulcanization accelerator is more than 0 phr, more preferably more than 0.1 phr, still more preferably more than 0.2 phr, particularly more than 0.3 phr, more particularly more than 0.4 phr, still more particularly more than 0.5 phr.

According to a preferred embodiment of the invention, the crosslinking system is based on sulfur, preferably the amount of sulfur is less than 2 phr, more preferably less than 1.9 phr, still more preferably less than 1.8 phr, particularly less than 1.7 phr, more particularly less than 1.6 phr, still more particularly less than 1.5 phr.

Use may be made, as vulcanization accelerator (primary or secondary) of any compound capable of acting as accelerator of the vulcanization of elastomer matrix, for instance, diene elastomers, in the presence of sulfur, in particular accelerators of the thiazoles type and their derivatives, accelerators of thiurams types. These accelerators are more preferably selected from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated to “MBTS”), N-cyclohexyl-2-benzothiazole sulfenamide (abbreviated to “CBS”), N,N-dicyclohexyl-2 benzothiazolesulfenamide (“DCBS”), N-tert-butyl-2-ben zothiazolesulfenamide (“TBBS”), N-tert-butyl-2 benzothiazolesulfenimide (“TBSI”), Tetrabenzylthiuram disulfide (“TBzTD”) and combinations thereof.

The rubber compositions according to the invention may be based on all or at least one portion of the usual additives generally used in the rubber compositions intended for rubber articles, such as, for example, protection agents other than anti-ozone waxes, such as antioxidants, plasticizing agents (for example, liquid plasticizers and hydrocarbon resins), tackifying resins or combinations thereof.

The rubber composition according to the invention may be manufactured in appropriate mixers using two successive preparation phases well known to a person skilled in the art: a first phase of thermomechanical working or kneading (referred to as “non-productive” phase) at high temperature, up to a maximum temperature of between 110℃ and 190℃, preferably between 130℃ and 180℃, followed by a second phase of mechanical working (referred to as “productive” phase) at a lower temperature, typically of less than 110℃, for example between 40℃ and 100℃, finishing phase during which the crosslinking or vulcanization system is incorporated.

A process which can be used for the manufacture of such compositions comprises, for example and preferably, the following steps:
- incorporating in the elastomer matrix, in a mixer, the reinforcing filler, the reinforcing resin, the anti-ozone wax, the zinc oxide, the stearic acid during a first stage (“non-productive” stage) everything being kneaded thermomechanically (for example in one or more steps) until a maximum temperature of between 110℃ and 190℃ is reached;
- cooling the combined mixture to a temperature of less than 100℃;
- subsequently incorporating, during a second stage (referred to as a "productive" stage), sulfur, a vulcanization accelerator(s), a vulcanization retarder(s) in the crosslinking system and a co-agent(s) of the reinforcing resin; and
- kneading everything up to a maximum temperature of less than 110℃.

By way of example, the first (non-productive) phase is carried out in a single thermomechanical stage during which all the necessary constituents are introduced into an appropriate mixer, such as a standard internal mixer, followed, in a second step, for example after kneading for 1 to 2 minutes, by the other additives, optional additional filler-covering agents or processing aids, with the exception of sulfur, the vulcanization accelerator(s) and the vulcanization retarder(s) in the crosslinking system and the co-agent(s) of the reinforcing resin. The total kneading time, in this non-productive phase, is preferably between 1 and 15 min.

After cooling the mixture thus obtained, sulfur, the vulcanization accelerator(s) and the vulcanization retarder(s) in the crosslinking system and the co-agent(s) of the reinforcing resin may be then incorporated at low temperature (for example, between 40℃ and 100℃), generally in an external mixer, such as an open mill; the combined mixture is then mixed (the second (productive) phase) for a few minutes, for example between 2 and 15 min.

The final composition thus obtained is subsequently calendered, for example in the form of a sheet or of a plaque, in particular for laboratory characterization, or else extruded in the form of a rubber profiled element which can be used directly as a rubber article.

The vulcanization (or curing) is carried out in a known way at a temperature generally of between 110℃ and 190℃ for a sufficient time which may vary, for example, between 5 and 90 min depending in particular on the curing temperature, the vulcanization system adopted and the vulcanization kinetics of the composition under consideration.

According to a preferred embodiment of the invention, an article comprises a rubber composition according to any one of the first to the fourteenth aspects.

According to a more preferred embodiment of the preferred embodiment, the article is a tire, a shoe, a conveyor or a caterpillar track.

A fifteenth aspect of the invention is a tire comprising a rubber composition according to any one of the first to the fourteenth aspects, preferably wherein the rubber composition is an internal rubber composition, more preferably wherein the internal rubber composition is adjacent to an external rubber composition, still more preferably wherein the internal rubber composition is adjacent to an external rubber composition and another internal rubber composition.

The tires of the invention are particularly intended to equip passenger motor vehicles, including 4×4 (four-wheel drive) vehicles and SUV (Sport Utility Vehicles) vehicles, and industrial vehicles particularly selected from vans and heavy duty vehicles (i.e., bus or heavy road transport vehicles (lorries, tractors, trailers)).

According to a preferred embodiment of the fifteenth aspect, the rubber composition according to the invention is an internal rubber composition intended here to mean any rubber part of the tire which is not open to the outside of the tire, in other words which is not in contact with the air or with an inflating gas and which is therefore situated in the actual inside of the tire structure; by way of examples, mention will notably be made of the rubber composition present in the bead zone, the carcass reinforcement or the crown reinforcement or belt, or therebetween of the tire, or therebetween, preferably the rubber composition according to the invention is an internal rubber composition adjacent to an rubber composition intended here to mean any part made of rubber of the tire which opens onto the outside of the tire, in other words which is in contact with the air or with an inflation gas; mention will in particular be made, as preferred examples, of the tread, side walls or airtight layer of the tire.

According to a more preferred embodiment of the fifteenth aspect or the above preferred embodiment, the internal rubber composition is adjacent to an external rubber composition, preferably the sidewalls of the tire are made of the external rubber composition.

According to a still more preferred embodiment of the above more preferred embodiment, the internal rubber composition is further adjacent to another internal rubber composition(s), preferably the carcass reinforcement, the beads or both of the tire is made of the other rubber composition(s).

The invention relates to the rubber compositions in the raw state (i.e., before curing) and in the cured state (i.e., after crosslinking or vulcanization).

The invention is further illustrated by the following non-limiting examples.

Example

In order to confirm the effect of the invention, five rubber compositions (C-1: a reference, C-2 to C-4: examples according to the invention, C-5: a comparative example) were used. The rubber compositions are based on a diene elastomer (NR, as an elastomer matrix), a reinforcing filler (a carbon black) and a reinforcing resin (a combination of diphenylolpropane and formophenolic novolac resin), zinc oxide and stearic acid with or without an anti-ozone wax. The formulations of the rubber compositions are shown in Table 1 with the amount of the various products expressed in phr.

Each rubber composition was produced as follows: the elastomer matrix, the reinforcing filler, the reinforcing resin, the anti-ozone wax, zinc oxide and stearic acid and the various other ingredients, with the exception of sulfur, a sulfured-vulcanization accelerator, and a vulcanization retarder (N-cyclohexylthiophthalimide) in the crosslinking system and a co-agent of the reinforcing resin (hexamethylenetetramine (HMT)), were successively introduced into an internal mixer having an initial vessel temperature of approximately 60℃; the mixer was thus approximately 70% full (% by volume). Thermomechanical working (non-productive phase) was then carried out in one stage, which lasts in total approximately 3 to 4 minutes, until a maximum “dropping” temperature of 165℃ was reached. The mixture thus obtained was recovered and cooled and then sulfur, the sulfured-vulcanization accelerator, and the vulcanization retarder (N-cyclohexylthiophthalimide) in the crosslinking system and the co-agent of the reinforcing resin were incorporated on an external mixer (homofinisher) at 20 to 30℃, everything being mixed (productive phase) for an appropriate time (for example, between 5 and 12 min).

The rubber compositions thus obtained were subsequently calendered, either in the form of sheets (thickness of 2 to 3 mm) or of fine sheets of rubber, for the measurement of their physical or mechanical properties, or in the form of profiled elements which could be used directly, after cutting, assembling, or both to the desired dimensions, for example as tire semi-finished products.

Tensile tests for the rubber compositions were done in order to determine the elasticity stresses, that is, the stiffness. Unless otherwise indicated, they were carried out in accordance with French Standard NF T 46-002 of September 1988. The nominal secant moduli (or apparent stresses, in MPa) at 50% elongation were measured in second elongation (i.e., after an accommodation cycle) at 23℃, with test specimens of the rubber compositions prepared by conventionally curing the rubber compositions (for example, at 150℃ for 60 minutes).

The results of the tensile tests are reported in Table 1, in relative units, the base 100 being selected for the reference (C-1) (it should be remembered that a value of greater than 100 indicates an improved performance), which indicate that the examples (C-2 to C-4) according to the invention have equivalent or superior stiffness, that means reasonable level on the stiffness, to that of the reference (C-1) or the comparative example (C-5).

Further, in order to determine the hysteresis loss, the rolling resistance tests in accordance with the following regulation were done with two radial carcass passenger vehicle tires (T-1: a reference, T-3: an example according to the invention). The regulation is “Regulation No 117 of the Economic Commission for Europe of the United Nations (UNECE) - Uniform provisions concerning the approval of tyres with regard to rolling sound emissions and/or to adhesion on wet surfaces and/or to rolling resistance”.

Furthermore, in order to determine the ozone resistance, the statistical ozone tests were done with the above two radial carcass passenger vehicle tires (T-1: the reference, T-3: the example according to the invention) mounted and inflated then subjected to load and placed in a cell under an ozone atmosphere for several weeks. The ozone concentration in the cell was maintained at 40 pphm and the temperature was 40℃.

The two radial carcass passenger vehicle tires (T-1: the reference, T-3: the example according to the invention) each comprising two beads designed to come into contact with a mounting rim, each bead comprising an annular reinforcing structure, two sidewalls extending the beads radially outwards, the two sidewalls meeting in a crown comprising a crown reinforcement surmounted by a tread, a carcass reinforcement extending from the beads through the sidewalls as far as the crown, the carcass reinforcement comprising a plurality of carcass reinforcing elements and being anchored in the two beads by being wrapped around the annular reinforcing structure so as to from within each bead, a main portion and a wrapped-around portion, each bead comprising a bead filler, the bead filler being situated radially on the outside of the annular reinforcing structure and partially between the main portion and the wrapped-around portion of the carcass reinforcement, each bead further comprising an outer strip portioned axially on the outside of the carcass reinforcement and of the bead filler, each outer strip extending radially between a radially inner end of the outer strip and a radially outer end of the outer strip, each outer strip adjacent to each sidewall around each radially outer end of each outer strip, and each outer strip made of each of the rubber compositions (C-1: the reference, C-3: the example according to the invention) were conventionally manufactured, and, in all respects, identical apart from the rubber compositions of the outer strips.

The “radially” means “in the radial direction” which is a direction perpendicular to the axis of the rotation of the tire.

The “axially” means “in the axial direction” which is a direction parallel to the axis of rotation of the tire.

The evaluation in the statistical ozone tests was done by the subjective visual check on the surfaces of the sidewalls adjacent to the outer strip made of the rubber compositions, and the example (T-3) according to the invention have equivalent rolling resistance (that means equivalent hysteresis loss) and superior ozone resistance performance (that means smaller numbers of cracks and shorter lengths of cracks) to that of the reference (T-1).

In conclusion, the rubber composition according to the invention allows an unexpectedly improved the ozone resistance of the rubber composition while maintaining reasonable levels on the stiffness and the hysteresis loss as the mechanical properties of the rubber composition.

(1) NR: Natural rubber (Peptised);
(2) Carbon black (ASTM grade N326 (designation according to ASTM D-1765) from Cabot);
(3) TDAE oil (“VivaTec 500” from H&R);
(4) Anti-ozone wax (“Varazon 6500” from Sasol);
(5) N-(1,3-dimethylbutyl)-N-phenyl-para-phenylenediamine (“Santoflex 6-PPD” from Flexsys);
(6) Stearic acid (“Pristerene 4931” from Uniqema);
(7) Zinc oxide (industrial grade from Umicore company);
(8) Rosin resin (“Abalyn” from Eastman);
(9) Combination of Diphenylolproprane (from Chimprom) and Formophenolic novolac resin (“Peracit 4536K” from Perstorp);
(10) Hexamethylenetetramine (from the company Degussa);
(11) N-(t-butyl)-2-benzothiazolesulfenamide (“Santocure TBBS” from Flexsys);
(12) N-cyclohexylthiophthalimide (“Vulkalent G” from Lanxess).

Claims

A rubber composition based on at least:
- an elastomer matrix;
- a reinforcing filler;
- a reinforcing resin;
- more than 0 phr and less than 5 phr of an anti-ozone wax; and
- a crosslinking system based on zinc oxide and stearic acid in amounts such that a ratio of the amount, in phr, of zinc oxide and of stearic acid is more than 3.
The rubber composition according to Claim 1, wherein the elastomer matrix comprises at least one diene elastomer selected from the group consisting of a polyisoprene, a polybutadiene, a butadiene copolymer, an isoprene copolymer and combinations thereof.
The rubber composition according to Claim 1 or Claim 2, wherein the elastomer matrix comprises more than 50 phr of a polyisoprene.
The rubber composition according to any one of Claims 1 to 3, wherein the amount of reinforcing filler is more than 20 phr.
The rubber composition according to any one of Claims 1 to 4, wherein the reinforcing filler comprises more than 50% by weight of a carbon black per 100% by weight of the reinforcing filler.
The rubber composition according to any one of Claims 1 to 5, wherein the amount of reinforcing resin is more than 1 phr.
The rubber composition according to any one of Claims 1 to 6, wherein the reinforcing resin is based on at least one reinforcing resin selected from the group consisting of a phenolic resin, an epoxy resin, a benzoxazine resin, a bismaleimide, a polyurethane resin and combinations thereof.
The rubber composition according to any one of Claims 1 to 7, wherein the reinforcing resin is based on at least one phenolic resin selected from the group consisting of at least one resin based on polyphenol, alkylphenol, aralkylphenol and combinations thereof.
The rubber composition according to any one of Claims 1 to 8, wherein the rubber composition is further based on at least one co-agent of the reinforcing resin.
The rubber composition according to Claim 9, wherein the amount of co-agent of the reinforcing resin is more than 1 phr.
The rubber composition according to Claim 9 or Claim 10, wherein the co-agent of the reinforcing resin is based on at least one resin co-agent selected from the group consisting of a methylene donor, a polyaldehyde, a polyamine, a polyimine, a polyamine, a polyaldimine, a polyketimine, an acid anhydride and combinations thereof.
The rubber composition according to any one of Claims 1 to 11, wherein the anti-ozone wax is based on from 50% to 75% of linear alkanes based on from 30 carbon atoms to 38 carbon atoms, with respect to the total amount of linear alkanes.
The rubber composition according to any one of Claims 1 to 12, wherein the amount of zinc oxide is more than 3 phr.
The rubber composition according to any one of Claims 1 to 13, wherein the amount of stearic acid is less than 3 phr.
A tire comprising a rubber composition according to any one of Claims 1 to 14, preferably wherein the rubber composition is an internal rubber composition, more preferably wherein the internal rubber composition is adjacent to an external rubber composition, still more preferably wherein the internal rubber composition is adjacent to an external rubber composition and another internal rubber composition.