Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/54—Silicon-containing compounds
  • C08K5/548—Silicon-containing compounds containing sulfur
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
  • B60C1/0016—Compositions of the tread
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/20—Compounding polymers with additives, e.g. colouring
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds
  • C08K5/37—Thiols
  • C08K5/375—Thiols containing six-membered aromatic rings

Definitions

• the present invention relates to the field of rubber compositions intended in particular for the manufacture of tires, and more especially for the manufacture of tire treads for motor vehicles.
• the subject of the invention is more particularly a sulfur-vulcanizable elastomeric composition containing a reinforcing filler and a specific coupling agent.
• Elastomeric compositions intended to form these treads are already known. They generally comprise, apart from a diene elastomer, a reinforcing filler. This reinforcing filler is generally carbon black or silica.
• the filler To obtain optimum reinforcement properties conferred by the filler, it is known that it is necessary for the filler to be present in the elastomer matrix in a final form that is both as finely divided as possible and as uniformly distributed as possible. However, such conditions cannot be met except if the filler has a very high capability, on the one hand, of being incorporated into the matrix during mixing with the elastomer and, on the other hand, of being uniformly dispersed within said matrix.
• silica particles have an annoying tendency to form agglomerations in the elastomer matrix. This has a deleterious effect on the reinforcing properties of the final product obtained after vulcanization. It is also problematic insofar as, by increasing the viscosity of the elastomer, silica, after it has been incorporated, makes the vulcanizable elastomeric composition difficult to work or to compound, especially when the non-sulfur-containing additives and the vulcanization system are being incorporated by mixing, or when the compound containing all the ingredients is being introduced into a vulcanization mold.
• silica in the manufacture of tire treads is particularly advantageous insofar as it is able to lower the rolling resistance and therefore give a substantial fuel saving.
• European patent application EP 0 501 227 mentions, for a sulfur-vulcanizable composition comprising a conjugated-diene copolymer reinforced by silica, the use of 12.8 parts by weight (per 100 parts of rubber) of a reinforcing agent comprising 6.4 parts by weight of a polysulfidic organosilane.
• the aim is therefore to find—and this is the object of the present invention—novel coupling agents of lower cost than Si-69 and ensuring optimum properties for tire treads, while still maintaining acceptable rheological properties for the processing and treatment of vulcanizable compositions, especially as regards their viscosity.
• the subject of the present invention is a sulfur-vulcanizable elastomeric composition comprising at least one diene elastomer and at least one reinforcing filler, characterized in that it can be obtained by a process comprising the mixing of said elastomer and said filler with an effective amount of a coupling agent consisting of a combination of:
• R is an alkyl radical containing 1 to 20, preferably 4 to 10, carbon atoms
• n and n′ are two integers, which may be identical or different, from 1 to 8, preferably from 1 to 4;
• p is an integer from 0 to 50, preferably from 0 to 20;
• composition according to the invention may comprise one or more diene elastomers.
• diene elastomers is understood more precisely to mean:
• (1) homopolymers obtained by the polymerization of a conjugated diene monomer having from 4 to 22 carbon atoms such as for example: 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 2-methyl-3-isopropyl-1,3-buta-diene, 1-phenyl-1,3-butadiene, 1,3-pentadiene and 2,4-hexadiene;
• a conjugated diene monomer having from 4 to 22 carbon atoms such as for example: 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-buta
• vinylaromatic monomers having from 8 to 20 carbon atoms such as for example: styrene, ortho-methylstyrene, meta-methylstyrene, para-methylstyrene, the commercial mixture “vinyltoluene”, para-tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene;
• vinyl nitrile monomers having from 3 to 12 carbon atoms, such as for example acrylonitrile and methacrylonitrile;
• acrylic ester monomers derived from acrylic acid or from methacrylic acid with alkanols having from 1 to 12 carbon atoms such as for example: methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and isobutyl methacrylate,
• copolymers may contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinylaromatic, vinyl nitrile and/or acrylic ester units;
• terpolymers obtained by the copolymerization of ethylene, an ⁇ -olefin having 3 to 6 carbon atoms and an unconjugated diene monomer having 6 to 12 carbon atoms such as for example elastomers obtained from ethylene, propylene and an unconjugated diene monomer of the aforementioned type, such as especially 1-4 hexadiene, ethylidene norbornene and dicyclopentadiene (EPDM elastomer);
• one or more elastomers chosen from polybutadiene and poly(styrene/butadiene), which are advantageously suitable for the manufacture of tire treads, are used.
• One or more reinforcing fillers such as a white filler and/or carbon black, may be used in the composition according to the invention.
• a white reinforcing filler is used.
• white reinforcing filler is understood to mean a white filler capable of reinforcing, by itself, without any means other than that of a coupling agent, a composition based on one or more elastomers of the natural or synthetic rubber type.
• the white reinforcing filler may be in the form of powder, microspheres, granules or beads.
• the white reinforcing filler generally consists of silica, aluminum or a mixture of these two species.
• the white reinforcing filler consists of silica, by itself or as a mixture with alumina.
• silica that can be used in the composition according to the invention, all precipitated or pyrogenic silicas known to those skilled in the art having a BET specific surface area of not less than 450 m 2 /g are suitable. It is preferred to use precipitated silicas, which may be conventional silicas or highly dispersible silicas.
• the expression “highly dispersible silica” is understood to mean any silica with a very high capability of deagglomerating and of dispersing in a polymeric matrix, as can be observed by electron microscopy or optical microscopy on thin sections.
• highly dispersible silicas mention may be made of those having a CTAB specific surface area of not less than 450 m 2 /g, preferably ranging from 30 to 400 m 2 /g, and particularly those described in patent U.S. Pat. No. 5,403,570 and patent applications WO-A-95/09127 and WO-A-95/09128.
• silica Perkasil KS 430 from Akzo
• silica BV3380 from Degussa
• the silicas Zeosil 1165 MP and 1115 MP from Rhodia
• the silica Hi-Sil 2000 from PPG
• the silicas Zeopol 8741 and 8745 from Huber.
• very suitable precipitated silicas are those having:
• CTAB specific surface area ranging from 100 to 240 m 2 /g, preferably 100 to 180 m 2 /g;
• a BET specific surface area ranging from 100 to 250 m 2 /g, preferably 100 to 190 m 2 /g;
• a BET specific surface area/CTAB specific surface area ratio ranging from 1.0 to 1.6.
• poly(alkylphenol) polysulfides of formula (I) have been known for a long time, and in particular are sold by Atofina under the brand name VULTAC®. They may be prepared by reacting a sulfur monochloride or dichloride with an alkylphenol at a temperature between 100 and 200° C. according to the following reaction:
• a mixture of compounds of formula (I) is used in which R is an alkyl radical containing at least one tertiary carbon via which R is linked to the aromatic ring.
• R is a tert-butyl or tert-pentyl radical.
• mixture of compounds of formula (I) a mixture in which the average value of n and of n′ is about 2 and the average value of p is about 5.
• the coupling agent in the composition according to the invention it is preferred to use a combination of the product of formula (I) and the product (II), in which the (I)/(II) weight ratio is from 1 to 3 and preferably about 2.
• the subject of the present invention is also the coupling agent as defined above.
• the product (II) called bis(triethoxysilylpropyl)tetra-sulfide is a mixture of compounds of formula: (EtO) 3 Si—(CH 2 ) 3 —S q —(CH 2 ) 3 —Si(OEt) 3 in which the average value of q is about 4.
• This product is commercially available, for example from Degussa AG (Germany) under the brand name Si-69®.
• the product (II) is used in the composition according to the invention in the form of a 50%/50% mixture by weight with carbon black.
• the composition according to the invention is obtained by mixing, with 100 parts by weight of diene elastomer(s):
• the method of preparing the sulfur-vulcanizable composition according to the invention further includes the incorporation of non-sulfur-containing additives normally used in elastomer compositions intended for the manufacture of treads, with the exception of the vulcanization system.
• non-sulfur-containing additives normally used in elastomer compositions intended for the manufacture of treads, with the exception of the vulcanization system.
• these may in particular be plasticizers, pigments, antioxidants, vulcanization activators, and naphthenic or aromatic oil extenders.
• the diene elastomer, the reinforcing filler, the products (I) and (II) and the non-sulfur-containing additives are subjected to mechanical working in any appropriate device, such as for example a mixer or an extruder, for the appropriate time, in such a way that it includes at least one thermal step at a temperature of between 130° C. and 170° C., preferably between 130° C. and 150° C.
• thermomechanical work varies according to the operating conditions adopted by those skilled in the art, and in particular to the chosen temperature within the range indicated above and to the nature and volume of the constituents subjected to the mechanical working.
• the essential point is that the mechanical working results in excellent dispersion of the filler, this being manifested, particularly if silica is used as filler, by a reduction in the size of the corresponding particles.
• thermomechanical work may vary from 1 minute to 20 minutes and may be determined by a person skilled in the art from his general knowledge and from measuring the properties of the composition when used in the form of a tire tread.
• thermomechanical work may comprise only a single thermomechanical step of appropriate duration, time and energy input, or it may comprise several thermomechanical steps possibly separated by at least one cooling step.
• a vulcanization system comprising in particular the sulfur and the vulcanization accelerators, by finish mechanical working, for example using an external mixer at a temperature of less than 100° C.
• a standard system is used as vulcanization system, for example one comprising, apart from sulfur, vulcanization accelerators such as sulfenamide and/or diphenylguanidine.
• the subject of the present invention is also a molded article that can be obtained by forming the composition obtained after incorporation of the vulcanization system and then heating.
• the composition After the composition has been formed in a suitable forming mold, for example by casting it, the composition is heated so as to vulcanize (or cure) it.
• this heating is carried out at a temperature generally ranging from 130° C. to 200° C., possibly with pressure applied, and for a sufficient time that may for example vary between 5 and 90 minutes, depending in particular on the cure temperature, the vulcanization system adopted and the vulcanization rate of the composition in question.
• tire treads are preferred because of their advantageous properties, namely tensile strength, wet grip and rolling resistance.
• composition based on poly(styrene/butadiene) (or SBR) and polybutadiene, reinforced by silica and containing 4 parts by weight of product (I) and 2 parts by weight of product (II).
• composition thus obtained was transferred to an external mixer of the two-roll mill type, each roll of which had a diameter of 300 mm and a length of 700 mm.
• the vulcanization system comprising sulfur and the two vulcanization accelerators, was then added to the composition at a temperature below 100° C. The mixing was continued for about 5 minutes.
• the Mooney viscosity was measured on the composition prepared as in A.
• the Mooney viscosity is the result of measuring the consistometric index carried out according to French Standard NF T43-005 published by Afnor (French Standardization Association). This measurement carried out on an unvulcanized rubber uses an apparatus called a “shear consistometer”.
• One portion of the composition was formed as a slab and then vulcanized at a temperature of 170° C. for 20 minutes. The slab was then cut into dumb bell test specimens (H2).
• composition was formed as test specimens of the Goodrich type (cylinders measuring 25 ⁇ 18 mm) which were then vulcanized at a temperature of 170° C. for 25 minutes.
• the 300% modulus/100% modulus ratio (or M300/M100), representative of the reinforcing index of the filler, was calculated from tensile tests carried out in accordance with French Standard NF T46-002 on dumb bell test specimens.
• tan ⁇ measured at a temperature of 0° C. and at a frequency of 10 Hz characterizes the wet grip: the higher the value of tan ⁇ at this temperature, the better the wet grip will be.
• the value of tan ⁇ measured at a temperature of 60° C. and a frequency of 10 Hz characterizes the rolling resistance: the lower the value of tan ⁇ at this temperature, the lower the rolling resistance and the better the fuel economy.
• Example 1 was repeated, with the contents of products (I) and (II) modified as indicated in Table I.
• Example 1 was repeated, but using as coupling agent only the product (II) with a content of 6.4 parts by weight (per 100 parts by weight of elastomers). This content corresponds to that of polysulfidic organosilane in patent EP 0 501 227 and to the amount of Si-69® usually introduced in the tire industry.
• styrene/butadiene copolymer prepared in solution, commercially available in the form of a 27.3% oil-extended elastomer, having a 25% styrene content, a 55% vinyl bond content, a 12% 1,4-trans bond content and an 8% 1,4-cis bond content.
• This product is sold under the brand name SBR Buna VSL 5525-1 by Bayer;
• antioxidant sold under the brand name Antiox 6PPD;
• poly(alkylphenol) polysulfide available under the name Vultac® TB7 from Atofina, namely a mixture of compounds of formula (I) in which R is a tert-butyl radical, n and n′ are each on average equal to about 2 and p is on average equal to about 5; and

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• 2003
  • 2003-06-16 FR FR0307193A patent/FR2856071B1/fr not_active Expired - Fee Related
• 2004
  • 2004-05-28 DE DE602004011935T patent/DE602004011935T2/de not_active Expired - Lifetime
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  • 2004-05-28 US US10/560,880 patent/US20060155026A1/en not_active Abandoned
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