Patent Application
20100012248
The present invention relates to a tire, in particular to a high-performance tire, to a tread band and to a crosslinkable elastomeric composition.
More in particular, the present invention relates to a tire, in particular to a high-performance tire, comprising at least one structural element including a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition comprising at least one styrene/1,3-butadiene copolymer, at least one diene elastomeric polymer other than the styrene/1,3-butadiene copolymer, at least one silica reinforcing filler, and at least one oil having a low content of polyaromatic hydrocarbons (PAH).
In a further aspect, the present invention also relates to a tread band including a crosslinkable elastomeric composition comprising at least one styrene/1,3-butadiene copolymer, at least one diene elastomeric polymer other than the styrene/1,3-butadiene copolymer, at least one silica reinforcing filler and at least one oil having a low content of polyaromatic hydrocarbons (PAH).
In a still further aspect, the present invention also relates to a crosslinkable elastomeric composition comprising at least one styrene/1,3-butadiene copolymer, at least one diene elastomeric polymer other than the styrene/1,3-butadiene copolymer, at least one silica reinforcing filler and at least one oil having a low content of polyaromatic hydrocarbons (PAH), as well as to a crosslinked manufactured article obtained by crosslinking said crosslinkable elastomeric composition.
With regard to high-performances tires, said tires, which are commonly referred to as “HP” or “UHP” (“High Performance” or “Ultra High Performance”) tires, are in particular those belonging to the classes “V” or “Z” which respectively provide for maximum speeds of between 210 Km/h and 240 Km/h and higher than 240 Km/h.
It is known to add process oils to both natural and synthetic elastomeric polymers for a number of reasons such as, for example, to reduce the mixing temperatures during processing, to decrease the viscosity of the elastomeric polymers and thereby facilitate milling, extruding and general workability of the crosslinkable elastomeric compositions which may contain other components, to reduce mill and calendering shrinkage, to aid the dispersion of fillers, to modify the physical properties of the crosslinked elastomeric compositions.
Typically, aromatic processing oils having a certain content of polycyclic aromatic (PCA) compounds [also known as polyaromatic hydrocarbons (PAH)], have been used.
In particular, it is known to use distillate aromatic extract oils (DAE-oils) in the manufacturing of tires, more in particular of tire tread bands, to improve tire performances. However, these DAE-oils have the disadvantages of containing a high amount of polyaromatic hydrocarbons (PAH) (approximately 400 ppm) which are ecologically harmful and under suspicion of causing cancer. Wear particles produced during car driving are an important factor for the pollution of the environment by DAE-oils.
Therefore several environmental agencies are demanding to eliminate DAE-oils from the market. For example, the European legislation classifies DAE-oils as “cancerogenic” and allocates the risk phrase “R45” (may cause cancer) to DAE-oils.
The European tire manufactures organization BLIC (Bureau the Liasons des Industries du Caoutchouc de l'U.E., Brussels) together with IISRP (European Section of the International Institute of Synthetic Rubber Producers, London) initiated a joint research program to look for alternatives. As a matter of fact they invited the oil companies to propose suitable candidates as DAE-oils alternatives.
In particular, mineral oils containing a dimethyl sulphoxide (DMSO) extract (determined by IP 346 test method) in an amount≦3 wt % are considered not carcinogenic and are suggested as DAE-oils alternatives. As representative of such special mineral oils may be mentioned, for example, mild extraction solvate oils (MES-oils) and treated distillate aromatic extract oils (T-DAE oils).
For example, J. E. Pocklington (“A safer alternative to aromatic process oils”; Tire Technology International 1998) suggests to replace the DAE-oils by different oils among which residual aromatic extract oils (RAE-oils) and MES-oils are cited. However, in that article, the use of RAE-oils is not recommended because of their limited availability.
However, the use of both MES-oils and TDAE-oils present some disadvantages as their chemical composition strongly differs from DAE-oils. To illustrate the different chemical compositions the typical carbons-distribution (Suncorrected) of MES-oils, TDAE-oils and DAE-oils are compared in the following table. The aromatic carbons (CA) content, the naphthene ring carbons (CN) content and the paraffin chain carbons (CP) content, was determined according to standard ASTM D2140-03 (Kurtz analysis) (the content is expressed in % by weight with respect to the total weight of the hydrocarbons contained in the oils).
Mainly the lower content of aromatic carbons (CA) in both MES-oils and TDAE-oils cause disadvantages in tires properties, in particular as regards their wet-skid behaviour, compared to DAE-oils. Therefore, these oils appear to be no particularly suitable for use in producing tire structural elements, more in particular, a tire tread band.
Other efforts have been made in the prior art to find alternative to DAE-oils.
For example, U.S. Pat. No. 5,504,113 discloses an oil composition which has a kinematic viscosity at 100° C. of from 32 cSt to 50 cSt and a DMSO extract of less than 3 wt % according to standard test IP 346. In particular, said oil may contain from 30 wt % to 55 wt %, e.g. in the range of from 30 wt % to 50 wt % (such as in the range of from 35 wt % to 48 wt %) total aromatic compounds based on the total weight of hydrocarbons contained in the oil. Of this, the DMSO extract present is less than 3 wt %, e.g. in the range of from 1 wt % to 3 wt %, such as in the range of from 1 wt % to 2 wt %, based on the total weight of hydrocarbons contained in the oil composition and determined according to standard test IP 346. The addition of said oils to rubber compositions is said to give the rubber compositions properties which result to be only slightly inferior with respect to the oils known in the prior art.
United States Patent Application 2002/0198296 discloses a rubber mixtures containing a terpolymer (NSBR) based on unsaturated olefinic nitrile, a vinyl aromatic compound and a conjugated diene, a non-polar rubber and a special mineral oil containing a DMSO extract in an amount≦3 wt % as determined according to standard test IP 346. Preferably, the special mineral oils used are MES-oils (Catenex SNR® is specifically disclosed) and TDAE-oils, as well as mineral oils such as naphthenic oils or hydrogenated naphthenic oils. The abovementioned rubber mixtures are said to have comparable or better technical qualities than rubber mixtures to which conventional aromatic mineral oils are added. In particular, the rubber mixtures are said to to have an improved wet-skid resistance.
United States Patent Application US 2005/0009978 discloses a pneumatic tire having a component comprising a vulcanizable rubber composition comprising, based on 100 parts by weight of elastomer (phr), from about 40 phr to about 90 phr of a solution polymerized styrene-butadiene having a styrene content of greater than 38 wt %; from about 10 phr to about 60 phr of at least one additional elastomer; and from about 10 phr to about 70 phr of a process oil having a glass transition temperature of from about −80° C. to about −40° C. and a DMSO extract of less than 3% by weight as determined according to standard test IP 346. Said special mineral oils may be selected from MES-oils (Catenex SNR® is specifically disclosed), TDAE-oils and heavy naphthenic type oils. The abovementioned pneumatic tire is said to have an excellent balance of rolling resistance and wet grip properties.
The Applicant has faced the problem of providing a tire, in particular a high-performance tire, having high wet and dry grip.
The Applicant has observed that the substitution of the aromatic oils (such as DAE-oils) by MES-oils or TDAE oils in the crosslinkable elastomeric compositions may show some drawbacks. In particular, the Applicant has observed that the use of said MES-oil or TDAE oils instead of DAE-oil does not allow to obtain a tire having high wet and dry grip.
The Applicant has now found that it is possible to obtain tires, in particular high-performance tires, showing high wet and dry grip by adding to the crosslinkable elastomeric compositions a RAE-oil. Said high wet and dry grip is obtained without negatively affecting the tires rolling resistance. Moreover, said high wet and dry grip is obtained without negatively affecting the static mechanical properties of the crosslinked elastomeric compositions. A still further advantageous aspect is the fact that said oil, having a low polyaromatic hydrocarbons (PAH) content (i.e. not higher than or equal to 10 ppm as determined by gas chromatography analysis presents a low toxicity and is not carcinogenic).
According to a first aspect, the present invention relates to a tire comprising at least one structural element including a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition comprising:
According to one preferred embodiment, the tire comprises:
For the purposes of the present invention and of the claims which follow, the term “phr” means the parts by weight of a given component of the crosslinkable elastomeric composition per 100 parts by weight of the elastomeric polymer(s).
For the purpose of the present description and of the claims which follow, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.
For the purpose of the present description and of the claims which follow the expression “RAE-oil” (residual aromatic extract oils) is referred to an oil obtained by a solvent extraction of a vacuum distillation residuum from crude oil subjected to a deasphalting treatment. A further explanation about the production process of a RAE-oil will follow.
According to a further aspect, the present invention also relates to a tread band including a crosslinkable elastomeric composition comprising:
According to a still further aspect, the present invention also relates to a crosslinkable elastomeric composition comprising:
According to one preferred embodiment, said crosslinkable elastomeric composition may further comprise (e) at least one silane coupling agent.
According to a further preferred embodiment, said crosslinkable elastomeric composition may further comprise at least one resin (f).
According to a still further aspect, the present invention also relates to a crosslinked manufactured article obtained by crosslinking said crosslinkable elastomeric composition.
According to one preferred embodiment, said crosslinkable elastomeric composition comprises from 50 phr to 90 phr of said at least one styrene/1,3-butadiene copolymer (a). More preferably, it comprises from 60 phr to 80 phr of said at least one styrene/1,3-butadiene copolymer (a).
According to a further preferred embodiment, said at least one styrene/1,3-butadiene copolymer (a) has a styrene content of from 10% to 50%. More preferably, said at least one styrene/1,3-butadiene copolymer (a) has a styrene content of from 20% to 40%. Still more preferably, said at least one styrene/1,3-butadiene copolymer (a) has a styrene content of from 25% to 35%.
According to a further preferred embodiment, said crosslinkable elastomeric composition comprises from 10 phr to 50 phr of said at least one diene elastomeric polymer other than the styrene/1,3-butadiene copolymer (b). More preferably, it comprises from 20 phr to 40 phr of said at least one diene elastomeric polymer other than the styrene/1,3-butadiene copolymer (b).
According to one preferred embodiment, said at least one diene elastomeric polymer other than the styrene/1,3-butadiene copolymer (b) may be selected from those commonly used in sulfur-crosslinkable elastomeric materials, that are particularly suitable for producing tires, that is to say from elastomeric polymers or copolymers with an unsaturated chain having a glass transition temperature (Tg) generally below 20° C., preferably in the range of from 0° C. to −110° C. These polymers or copolymers may be of natural origin or may be obtained by solution polymerization, emulsion polymerization or gas-phase polymerization of one or more conjugated diolefins, optionally blended with at least one comonomer selected from monovinylarenes and/or polar comonomers in an amount of not more than 60% by weight.
The conjugated diolefins generally contain from 4 to 12, preferably from 4 to 8 carbon atoms, and may be selected, for example, from the group comprising: 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene, or mixtures thereof. 1,3-butadiene or isoprene are particularly preferred.
Monovinylarenes which may optionally be used as comonomers generally contain from 8 to 20, preferably from 8 to 12 carbon atoms, and may be selected, for example, from: styrene; 1-vinyinaphthalene; 2-vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl derivatives of styrene such as, for example, α-methylstyrene, 3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-ptolylstyrene, 4-(4-phenylbutyl)styrene, or mixtures thereof. Styrene is particularly preferred.
Polar comonomers which may optionally be used may be selected, for example, from: vinylpyridine, vinylquinoline, acrylic acid and alkylacrylic acid esters, nitriles, or mixtures thereof, such as, for example, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, or mixtures thereof.
Preferably, said at least one diene elastomeric polymer other than the styrene/1,3-butadiene copolymer (b) may be selected, for example, from: cis-1,4-polyisoprene (natural or synthetic, preferably natural rubber), 3,4-polyisoprene, polybutadiene (in particular polybutadiene with a high 1,4-cis content and a low vinyl content), optionally halogenated isoprene/isobutene copolymers, 1,3-butadiene/acrylonitrile copolymers, styrene/isoprene/1,3-butadiene copolymers, styrene/1,3-butadiene/acrylonitrile copolymers, or mixtures thereof. Polybutadiene, in particular, polybutadiene with a high 1,4-cis content and a low vinyl content, is particularly preferred. More preferably, said polybutadiene has a 1,4-cis content of more than 90% and a vinyl content of less than 5%.
The above reported crosslinkable elastomeric composition may optionally comprise at least one diene elastomeric polymer functionalized by reaction with suitable terminating agents or coupling agents. In particular, the diene elastomeric polymers obtained by anionic polymerization in the presence of an organometallic initiator (in particular an organolithium initiator) may be functionalized by reacting the residual organometallic groups derived from the initiator with suitable terminating agents or coupling agents such as, for example, imines, carbodiimides, alkyltin halides, substituted benzophenones, alkoxysilanes or aryloxysilanes (see, for example, European Patent EP 451,604, or U.S. Pat. No. 4,742,124 and U.S. Pat. No. 4,550,142). According to one preferred embodiment, said crosslinkable elastomeric composition comprises from 70 phr to 90 phr of said at least one silica reinforcing filler (c). More preferably, it comprises from 75 phr to 85 phr of said at least one silica reinforcing filler.
According to a further preferred embodiment, said at least one silica reinforcing filler (c) may be selected from precipitated amorphous silica, wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), fumed silica, or mixtures thereof. Precipitated amorphous silica, hydrated silica, are preferred, in particular those having a BET surface area (measured according to ISO standard 5794/1) of from 50 m2/g to 500 m2/g, preferably of from 70 m2/g to 200 m2/g.
According to one preferred embodiment, said crosslinkable elastomeric composition comprises from 20 phr to 60 phr of said at least one RAE-oil (d). More preferably, it comprises from 25 phr to 50 phr, even more preferably from 30 phr to 40 phr, of said at least one RAE-oil (d).
According to one preferred embodiment, said at least one RAE-oil (d) has the following carbons-distribution:
According to an even more preferred embodiment, said at least one RAE-oil (d) has the following carbons-distribution:
The aromatic carbons (CA) content, the naphthene ring carbons (CN) content and the paraffin chain carbons (CP) content, was determined according to standard ASTM D2140-03 (Kurtz analysis) (the content is expressed in % by weight with respect to the total weight of the hydrocarbons contained in the oils).
The PAH-content was measured by a gas chromatography analysis. Said at least one RAE-oil (d) may be produced by processes which are well known in the art. For example, said at least one RAE-oil (d) may be produced by a process comprising the following steps:
Specific examples of deasphalting agents which may be advantageously used in step (ii) are: propane, n-butane, iso-butane, pentane, or mixtures thereof.
Specific example of solvent which may be advantageously used in step (iv) are: furfural, N-methyl-2-pyrrolidone, phenol, or mixtures thereof, optionally admixed with water.
Examples of RAE-oils (d) which may be used in the present invention and which are currently commercially available are the products Dealen® D52 KF and Shell Flavex® 595 from Shell.
As disclosed above, said crosslinkable elastomeric composition may further comprise (e) at least one silane coupling agent capable of interacting with the silica and of linking it to the elastomeric polymer during the vulcanization.
Coupling agents that are preferably used are those based on silane which may be identified, for example, by the following structural formula (I):
(R)3Si—CtH2t—X (I)
wherein the groups R, which may be equal or different from each other, are selected from: alkyl, alkoxy or aryloxy groups or from halogen atoms, on condition that at least one of the groups R is an alkoxy or aryloxy group; t is an integer of from 1 to 6 extremes included; X is a group selected from: nitroso, mercapto, amino, epoxide, vinyl, imide, chloro, —(S)uCtH2t—Si—(R)3 or or —S—COR in which u and t are integers of from 1 to 6 extremes included and the groups R are defined as reported above.
Among the coupling agents that are particularly preferred are bis(3-triethoxysilylpropyl)tetrasulphide and bis(3-triethoxysilylpropyl)disulphide. Said coupling agents may be used as such or as a suitable mixture with an inert filler (for example, carbon black) so as to facilitate their incorporation into the crosslinkable elastomeric composition.
According to one preferred embodiment, said at least one silane coupling agent (e) is present in the crosslinkable elastomeric composition in an amount of from 0 phr to 10 phr, preferably of from 4 phr to 8 phr.
As disclosed above, said crosslinkable elastomeric composition may further comprise (f) at least one resin. Preferably, said at least one resin (f) may be selected, for example, from α-methyl-styrene resins, phenolic resins. cumarone indene resins, or mixture thereof.
According to one preferred embodiment, said at least one resin (e is present in the crosslinkable elastomeric composition in an amount of from 0 phr to 15 phr, preferably of from 7 phr to 12 phr.
At least one additional reinforcing filler may advantageously be added to the above reported crosslinkable elastomeric composition, in an amount generally of from 0 phr to 120 phr, preferably of from 20 phr to 90 phr. Said at least one additional reinforcing filler may be selected from those commonly used for crosslinked manufactured articles, in particular for tires, such as, for example, carbon black, alumina, calcium carbonate, kaolin, or mixtures thereof. Carbon black is particularly preferred.
The types of carbon black which may be used according to the present invention may be selected from those conventionally used in the production of tires, generally having a surface area of not less than 20 m2/g (determined by CTAB absorption as described in ISO standard 6810).
The crosslinkable elastomeric composition above reported may be vulcanized according to known techniques, in particular with sulfur-based vulcanizing systems commonly used for elastomeric polymers. To this end, in the composition, after one or more steps of thermomechanical processing, a sulfur-based vulcanizing agent is incorporated together with vulcanization accelerators. In the final processing step, the temperature is generally kept below 120° C. and preferably below 100° C., so as to avoid any unwanted pre-crosslinking phenomena.
The vulcanizing agent most advantageously used is sulfur, or molecules containing sulfur (sulfur donors), with accelerators and activators known to those skilled in the art.
Activators that are particularly effective are zinc compounds, and in particular ZnO, ZnCO3, zinc salts of saturated or unsaturated fatty acids containing from 8 to 18 carbon atoms, such as, for example, zinc stearate, which are preferably formed in situ in the elastomeric composition from ZnO and fatty acid, and also BiO, PbO, Pb3O4, PbO2, or mixtures thereof.
Accelerators that are commonly used may be selected from: dithiocarbamates, guanidine, thiourea, thiazoles, sulphenamides, thiurams, amines, xanthates, or mixtures thereof.
Said crosslinkable elastomeric composition may comprise other commonly used additives selected on the basis of the specific application for which the crosslinkable elastomeric composition is intended. For example, the following may be added to said crosslinkable elastomeric composition: antioxidants, anti-ageing agents, plasticizers, adhesives, antiozonants (in particular of the p-phenylenediamine type), waxes, fibres (for example Kevlar® pulp), or mixtures thereof.
The above reported crosslinkable elastomeric composition may be prepared by mixing together the elastomeric base components, the silica reinforcing filler and the oil, with the other reinforcing fillers and the other additives optionally present, according to techniques known in the art. The mixing may be carried out, for example, using an open mixer of open-mill type, or an internal mixer of the type with tangential rotors (Banbury) or with interlocking rotors (Intermix), or in continuous mixers of Ko-Kneader type (Buss), or of corotating or counter-rotating twin-screw type.
The present invention will now be illustrated in further detail by means of a number of illustrative embodiments, with reference to the attached
“a” indicates an axial direction and “r” indicates a radial direction. For simplicity,
The tire (100) comprises at least one carcass ply (101), the opposite lateral edges of which are associated with respective bead structures comprising at least one bead core (102) and at least one bead filler (104). The association between the carcass ply (101) and the bead core (102) is achieved here by folding back the opposite lateral edges of the carcass ply (101) around the bead core (102) so as to form the so-called carcass back-fold (101a) as shown in
Alternatively, the conventional bead core (102) may be replaced with at least one annular insert formed from rubberized wires arranged in concentric coils (not represented in
The carcass ply (101) generally consists of a plurality of reinforcing cords arranged parallel to each other and at least partially coated with a layer of a crosslinked elastomeric material. These reinforcing cords are usually made of textile fibres, for example rayon, nylon or polyethylene terephthalate, or of steel wires stranded together, coated with a metal alloy (for example copper/zinc, zinc/manganese, zinc/molybdenum/cobalt alloys, and the like).
The carcass ply (101) is usually of radial type, i.e. it incorporates reinforcing cords arranged in a substantially perpendicular direction relative to a circumferential direction. The core (102) is enclosed in a bead (103), defined along an inner circumferential edge of the tire (100), with which the tire engages on a rim (not represented in
A belt structure (106) is applied along the circumference of the carcass ply (101). In the particular embodiment in
A side wall (108) is also applied externally onto the carcass ply (101), this side wall extending, in an axially external position, from the bead (103) to the end of the belt structure (106).
A tread band (109), which may be made according to the present invention, whose lateral edges are connected to the side walls (108), is applied circumferentially in a position radially external to the belt structure (106). Externally, the tread band (109) has a rolling surface (109a) designed to come into contact with the ground. Circumferential grooves which are connected by transverse notches (not represented in
A tread underlayer (111) is placed between the belt structure (106) and the tread band (109).
As represented in
In
A strip made of a crosslinked elastomeric material (110), commonly known as a “mini-side wall”, may optionally be present in the connecting zone between the side walls (108) and the tread band (109), this mini-side wall generally being obtained by co-extrusion with the tread band and allowing an improvement in the mechanical interaction between the tread band (109) and the side walls (108). Alternatively, the end portion of the side wall (108) directly covers the lateral edge of the tread band (109).
In the case of tubeless tires, a rubber layer (112) generally known as a liner, which provides the necessary impermeability to the inflation air of the tire, may also be provided in an inner position relative to the carcass ply (101).
The process for producing the tire according to the present invention may be carried out according to techniques and using apparatus that are known in the art, as described, for example, in European Patents EP 199,064, or in U.S. Pat. No. 4,872,822 or U.S. Pat. No. 4,768,937, said process including at least one stage of manufacturing the crude tire and at least one stage of vulcanizing this tire.
More particularly, the process for producing the tire comprises the steps of preparing, beforehand and separately from each other, a series of semi-finished products corresponding to the various structural elements of the tire (carcass plies, belt structure, bead wires, fillers, sidewalls and tread band) which are then combined together using a suitable manufacturing machine. Next, the subsequent vulcanization step welds the abovementioned semi-finished products together to give a monolithic block, i.e. the finished tire.
The step of preparing the abovementioned semi-finished products will be preceded by a step of preparing and moulding the various crosslinkable elastomeric compositions, of which said semi-finished products are made, according to conventional techniques.
The crude tire thus obtained is then passed to the subsequent steps of moulding and vulcanization. To this end, a vulcanization mould is used which is designed to receive the tire being processed inside a moulding cavity having walls which are countermoulded to define the outer surface of the tire when the vulcanization is complete.
Alternative processes for producing a tire or parts of a tire without using semi-finished products are disclosed, for example, in the above-mentioned European Patent Application EP 928,680 or EP 928,702.
According to one preferred embodiment, said structural elements are formed by a plurality of coils of a continuous elongated element. Said elongated element may be produced, for example, by extruding the crosslinkable elastomeric composition above disclosed. Preferably, said structural elements are assembled onto a support.
For the purposes of the present description and of the claims which follow, the term “support” is used to indicate the following devices:
Further details regarding said devices and the methods of forming and/or depositing the structural elements of the tire on a support are described, for example, in International Patent Application WO 01/36185 or in European Patent EP 976,536 in the name of the Applicant, or in European Patent Application: EP 968,814, EP 1,201,414, or EP 1,211,057. The crude tire can be moulded by introducing a pressurized fluid into the space defined by the inner surface of the tire, so as to press the outer surface of the crude tire against the walls of the moulding cavity. In one of the moulding methods widely practised, a vulcanization chamber made of elastomeric material, filled with steam and/or another fluid under pressure, is inflated inside the tire closed inside the moulding cavity. In this way, the crude tire is pushed against the inner walls of the moulding cavity, thus obtaining the desired moulding. Alternatively, the moulding may be carried out without an inflatable vulcanization chamber, by providing inside the tire a toroidal metal support shaped according to the configuration of the inner surface of the tire to be obtained as described, for example, in Europen Patent EP 1,189,744.
At this point, the step of vulcanizing the crude tire is carried out. To this end, the outer wall of the vulcanization mould is placed in contact with a heating fluid (generally steam) such that the outer wall reaches a maximum temperature generally of from 100° C. to 230° C. Simultaneously, the inner surface of the tire is heated to the vulcanization temperature using the same pressureized fluid used to press the tire against the walls of the moulding cavity, heated to a maximum temperature of from 100° C. to 250° C. The time required to obtain a satisfactory degree of vulcanization throughout the mass of the elastomeric material may vary in general of from 3 min to 90 min and depends mainly on the dimensions of the tire. When the vulcanization is complete, the tire is removed from the vulcanization mould.
The present invention will be further illustrated below by means of a number of preparation examples, which are given for purely indicative purposes and without any limitation of this invention.
The elastomeric compositions given in Table 2 were prepared as follows (the amounts of the various components are given in phr).
All the components, except sulfur and accelerators (DPG 80, CBS), were mixed together in an internal mixer (model Pomini PL 1.6) for about 5 min (1st Step). As soon as the temperature reached 145±5° C., the elastomeric composition was discharged. The sulfur and accelerators (DPG 80, CBS), were then added and the mixing was carried out in an open roll mixer (2nd Step).
The compounds were brought to the same hardnesses by using different amounts of free oils. Different amounts of free oils were chosen because physical data of tread compounds may only be compared if said tread compounds exhibit equal hardness.
The Mooney viscosity ML(1+4) at 100° C. was measured, according to ISO standard 289-1:1994, on the non-crosslinked elastomeric compositions obtained as described above. The results obtained are given in Table 3.
Said elastomeric compositions were also submitted to a MDR rheometric analysis using a MDR rheometer from Monsanto, the tests being run at 170° C. for 24 minutes, with an oscillation frequency of 1.66 Hz (100 oscillations per minute) and an oscillation amplitude of +0.5°. The results obtained are given in Table 3.
The static mechanical properties according to Standard ISO 37:1994 as well as hardness in IRHD degrees (at 23° C.) according to ISO standard 48:1994, were measured on samples of the abovementioned elastomeric compositions vulcanized at 170° C. for 10 min. The results obtained are given in Table 3.
Table 3 also shows the dynamic mechanical properties, measured using an Instron dynamic device in the traction-compression mode according to the following methods. A test piece of the crosslinked elastomeric composition (vulcanized at 170° C. for 10 min) having a cylindrical form (length=25 mm; diameter=12 mm), compression-preloaded up to a 25% longitudinal deformation with respect to the initial length, and kept at the prefixed temperature (−10° C., 0° C., 23° C., or 70° C.) for the whole duration of the test, was submitted to a dynamic sinusoidal strain having an amplitude of ±3.5% with respect to the length under pre-load, with a 10 Hz frequency. The dynamic mechanical properties are expressed in terms of dynamic elastic modulus (E′) and Tan delta (loss factor) values. The Tan delta value is calculated as a ratio between viscous modulus (E″) and elastic modulus (E′).
Table 3 also show the DIN abrasion: the data (expressed in mm3) correspond to the amount of elastomeric composition removed by operating under the standard conditions given in DIN standard 53516.
The data above reported clearly show that remarkable differences between the different oils occur in the dynamic physical data of the elastomeric compositions so obtained. As a matter of fact, while the MES-oil (Example 3) and the TDAE-oil (Example 2) exhibit much lower Tan delta values at −10° C. and 0° C., the RAE-oils (Examples 4-5) show higher values even than the DAE-oil (Example 1). Because a higher Tan delta value at −10° C. and 0° C. predicts a higher wet grip performance it can be expected that the RAE-oils lead to an improved wet behavior of the tire compared even to a tire produced using a DAE-oil. Also at 23° C. the tan delta values of RAE-oils, which predict dry grip, are higher than the value of the DAE-oil and much higher than the values of the MES-oil and the TDAE-oil. It follows that the use of RAE-oils allows to obtain tires having higher wet and dry grip than tires produced using usual aromatic oils.
The Tan delta values at 70° C., which predict rolling resistance, are not higher for the RAE-oils (Examples 4-5) compared to the usual aromatic oils (Examples 1-3). Since a higher Tan delta value at 70° C. is correlated with a higher rolling resistance, one can deduce that using a RAE-oil does not negatively influence the rolling resistance of the tire.
Also the E′ values are not changed by the substitution of usual aromatic oils (Examples 1-3) by RAE-oils (Examples 4-5). Further, rheometric properties, static mechanical properties and DIN abrasion of all elastomeric compositions are similar: consequently, the use of RAE-oils do not negatively affect said properties.
| Number | Date | Country | Kind |
|---|---|---|---|
| 05016608.1 | Jul 2005 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/064170 | 7/12/2006 | WO | 00 | 4/16/2009 |
