Improved electrical conductivity of silica-filled rubber compositions

ES 2 228 526 T3

DESCRIPTION

Improved electrical conductivity of silica-filled rubber compositions.

Field of the invention

This invention relates generally to silica-filled rubber compositions, and more particularly, to silica-filled rubber compositions containing poly (alkylene oxide) compounds having dissolved alkali metal salts therein to improve performance. electrical conductivity of rubber compositions. These rubber compositions are particularly useful in tires as silica-reinforced tread compositions and are particularly suitable for the prevention or dissipation of any electrostatic charge that could build up in the tire. The invention also relates to a method for dissipating electrostatic charges in silica-filled rubber compositions and, more particularly, for preventing the build-up of electrostatic charges in tires having silica-reinforced tread compositions. .

Background of the invention

It is known that electrostatic charges can be produced by any of a number of different pathways within a motor vehicle. For example, mechanical and electrical components that operate within the motor vehicle such as, for example, a rotating shaft within a bearing, can result in electrostatic charge that is generated within the vehicle, or even tire friction from Rubber rolling on the road can generate an electrostatic charge. Typically, these charges are dissipated through rubber tires contacting the ground since tires typically include a sufficient amount of electrically conductive materials in them. When such dissipation does not take place, interference with electronic components within the motor vehicle could occur. In addition, a static shock could be experienced by the passengers of the vehicle when they get into the vehicle. Such high electrical loads can also lead to safety hazards when refueling the vehicle.

Although rubber tires have typically acted as a suitable conductor for dissipating such static charges produced from mechanical or electrical components of a motor vehicle, the use of less conductive materials in tires has resulted in a decrease in the ability of tires to effectively dissipate these static charges. This is particularly true of rubber tire compositions that use silica as a reinforcing filler. The advantages of silica-filled tires are well known in the art as silica has been found to provide excellent wet traction, excellent performance, and low rolling resistance in tires, while reducing hysteresis.

While silica-filled tires are advantageous, attempts have been made to produce tires, and in particular tire tread compositions, which are silica-filled, or at least partially silica-filled and which properly dissipate static electricity.

Initial attempts at increasing the conductivity of tires, including those silica-loaded tread compositions have focused on the use of electromechanical means as an alternative conduit to dissipate electrostatic charges. For example, US Patent No. 5,518,055 shows a tire having an electrostatic discharge ring positioned on at least one shoulder of the tire. The discharge ring exhibits a relatively low volume resistivity, which is of the order of 100 megohm cm. The relief ring is critically positioned so that it contacts the ground surface and dissipates the static charge generated within the internal parts of the tire. Similarly, European Patent Application Nos. 681,931 A1 and 718,126 A2 show tires or tire treads having a thin conductive layer on the outermost part of the tread. In one case, the thin layer extends continuously in a circumferential direction over the tread of the tire; and in another embodiment the conductive portion has a width that is 15 percent of the ply width of the tire.

European Patent Application Nos. 0705722 A1 and 0732229 A1 show silica reinforced rubber treads containing an overcoat or thin layer containing a quantitative amount of electrically conductive carbon black. In one embodiment, the outer top layer extends along the outer surface of the tread and in an alternative embodiment the outer layer extends only over the outer portion or peripheral ends of the tread surface that is intends to be in contact with the ground.

Similarly, European patent applications 0718127 A1 and 0747243 A1 show tires that have one or more layers of tread that provide contact with the ground and that are electrically conductive. These layers also extend radially inward to contact the pleats of the tire body or bead area of ​​the tire.

More recently, attempts have been made using chemical additives to improve electrical conductivity

ES 2 228 526 T3 of rubber compositions. For example, phosphoric ester nonionic surfactants have been used in rubber tire compounds to improve electrical conductivity. A rubber composition exhibiting improved conductivity properties is disclosed in US Patent No. 5,714,533 that includes a rubber component, a filler such as silica, and a nonionic surfactant or phosphoric ester. Typical examples of the nonionic surfactant are ethylene oxide adducts of 2 to 30 moles relative to linear saturated or unsaturated, cyclic or branched aliphatic alcohol, monohydric or polyhydric, having 6 to 25 carbon atoms, or oxide adducts of ethylene from 2 to 30 moles relative to alkylphenol, while representative phosphoric esters include those represented by the following formulas (I) and (II):

OR

II

R'OPO - (CH₂CH₂OR)_whatH

O - (CH₂CH₂OR)_rH (I) in which R represents an aliphatic, linear or branched, and saturated or unsaturated hydrocarbon group having 8 to 25 carbon atoms or an aryl group; and q and r are each an integer that satisfies the relation q + r = 1 to 30, or

OR

II

R'OPO - (CH2CH2O) qH

OR "(II) in which R 'and R" each represent a linear or branched, and saturated or unsaturated aliphatic hydrocarbon group having from 8 to 25 carbon atoms or an aryl group and may be the same or different; ys is an integer from 1 to 30.

The addition of other chemical ingredients, such as carbon black fibers or ultrafine carbon fibrils, has been described to provide superior reinforcement and electrical conductivity compared to conventional carbon black reinforcing fillers.

In addition, other chemical additives, namely polyoxyethylene phenol derivatives, commercially available under the trade name "Triton", are believed to have been tried as electrically conductive additives. However, it has been found that the use of poly (alkylene oxide) derivatives alone does not provide a significant antistatic effect (as noted in column 7, lines 40-46 of US Patent No. 5,714,533) or, if they are capable of providing the desired effect, they will peel off the rubber quickly.

German Patent Application No. 19726728 A1 describes rubber compositions for use in tire treads comprising an elastomer, for example NBR rubber, silica, lithium perchlorate and an alkylene glycol, for example diethylene glycol. This document does not contain any disclosure regarding a polymer containing polyalkylene oxide.

European Patent Application No. 0909785 A1 describes polymeric compositions comprising an elastomer, for example an EPDN rubber, sodium perchlorate and a poly (alkylene glycol) ester, for example poly (ethylene glycol) laurate. This document does not contain any disclosure regarding silica or a poly (alkylene oxide) containing polymer.

Summary of the invention

Thus, a need continues to exist for an effective silica-reinforced tread composition, which will dissipate electrostatic charges while maintaining or improving the physical properties currently associated with silica-filled and non-silica-filled tire tread compositions. it will come off the composition. It is further desired that the means by which the electrical conductivity of the tread composition is improved also act as a dispersing agent for silica.

One aspect of the present invention is to provide a silica reinforced rubber composition exhibiting suitable electrostatic dissipation properties.

Another aspect of the invention is to provide a silica reinforced rubber composition, as above, suitable for use in a tire tread composition.

Still another aspect of the present invention is to provide the rubber composition, as above, in which the means used to increase the electrical conductivity of the rubber composition further acts as a dispersing agent for the silica.

ES 2 228 526 T3

Another aspect of the present invention is to provide a rubber composition that contains an additive that does not come off the composition.

Another aspect of the present invention is to provide tires that exhibit improved electrostatic dissipation properties.

Another aspect of the present invention is to provide a method for the dissipation of electrostatic charges in tires having silica-reinforced tread compositions.

In general, the present invention provides a tire tread composition exhibiting improved electrical conductivity properties comprising 100 parts by weight of a vulcanizable elastomer suitable for use in a tire; 1 to 100 parts by weight of a silica reinforcing filler, per 100 parts of the elastomer; and 0.1 to 15 parts by weight of an electrically conductive additive containing a poly (alkylene oxide) containing polymer having an alkali metal salt dissolved therein, per 100 parts of the elastomer.

The present invention also includes tires exhibiting improved electrostatic dissipation using the above tire tread composition.

Furthermore, the present invention includes a method of dissipating the electrostatic charge of air tires comprising the step of applying to a tire carcass before curing, a tread of the above tread composition.

Embodiments of the invention

The present invention relates to the use of a small amount of an additive suitable for improving the electrical conductivity of a load-reinforced tire tread composition. Reinforcing fillers such as carbon black and silica are known to increase the modulus of elastomeric polymers to which they are added. To be effective, a good bond must take place between the polymer (rubber) and the filler, which is referred to as blended rubber. Although silica is particularly effective as a reinforcing filler by reducing the hysteresis of the rubber into which it is incorporated, it has also been found that silica-filled vulcanizable rubber tread compounds do not particularly adequately dissipate static charges. generated when the vehicle is in motion.

The present invention seeks to dissipate these electrostatic charges by incorporating into the silica-loaded rubber composition, preferably used as a tire tread composition, of a small amount of a poly (alkylene oxide) containing polymer having a hygroscopic salt dissolved therein, which has been found to improve the electrical conductivity of the rubber composition. It has been found that by adding 0.1 to 15 parts by weight of this type of electrically conductive additive, per 100 parts by weight of rubber (phr) in the tire tread rubber formulation, a significant increase (of approximately two orders of magnitude) in the electrical conductivity of the silica-loaded part is obtained without appreciably compromising the physical properties of the cured treads and the performance of tires produced with such treads.

Furthermore, it has been found that this additive can further act as a dispersing agent for silica.

Furthermore, in cases where the carbon black has been finely dispersed, an appreciable loss of electrical conductivity can be seen in the carbon black loaded composition. It is believed that the use of these electrically conductive additives will also increase the conductivity of the well-dispersed carbon black within the tire tread composition such that other technical improvements associated with the use of well-dispersed carbon black can be made.

The term "phr", as used throughout the specification, and in accordance with conventional practice in the art, refers to parts of a respective material "per 100 parts by weight of rubber or elastomer". It will further be appreciated that the terms "rubber" and "elastomer", as used throughout the specification, may be used interchangeably, unless otherwise prescribed, and generally refer to the rubber or polymer matrix that has been compounded, combined, or mixed with different materials. Such terms are believed to be widely known to those skilled in the rubber compounding and rubber compounding arts.

Typically, in the formulation of vulcanizable rubber compounds for tread parts, a polymerized elastomer, for example, polybutadiene, polyisopropene and the like, and copolymers and terpolymers thereof are composed with monovinyl aromatic compounds such as styrene. , alpha methylstyrene and the like, or trines such as myrcene, to form the rubber part. Thus, elastomers include diene homopolymers, A, and copolymers and terpolymers thereof with monovinyl aromatic polymers, B. Examples of diene homopolymers are those prepared from diolefin monomers having 4 to 12 carbon atoms. Examples of vinyl aromatic polymers are those prepared from monomers having 8 to 20 carbon atoms. Examples of conjugated diene monomers and the like useful in the present invention include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and 1,3-hexadiene, and aromatic vinyl monomers. They include styrene, α-methylstyrene, p-methylstyrene, vinyltoluenes, and vinylnaphthalenes. Monomer

ES 2 228 526 T3 of the conjugated diene and the vinyl aromatic monomer are normally used at weight ratios of 90:10 to 55:45, preferably 80:20 to 65:35.

Preferred elastomers include diene homopolymers such as polybutadiene and polyisoprene, and copolymers such as styrene butadiene rubber (SBR). The copolymers may comprise from 99 to 55 percent by weight of diene units and from 1 to 45 percent by weight of aromatic monovinyl or triene units, totaling 100 percent. The polymers and copolymers of the present invention may have 1,2-microstructure contents ranging from 10 to 80 percent, with contents of the preferred 1,2-microstructure polymers or copolymers ranging from 25 to 65 percent, based on the content of diene. The molecular weight of the polymer produced in accordance with the present invention is preferably such that a proton inactivated sample will show a Mooney viscosity of the gum (ML₄/ 100 ° C) from 2 to 150. The copolymers and terpolymers are preferably random polymers that result from a simultaneous copolymerization of the monomers, as is known in the art. Also included are non-functionalized cis-polybutadiene monomers, ethylene-propylene-diene (EPDM), emulsion styrene butadiene rubber, styrene isoprene butadiene rubber (SIB), and natural rubber.

The above-described copolymers and terpolymers of conjugated dienes and their process of preparation are well known in the rubber and polymer arts. Many of the polymers are commercially available. It is to be understood that the practice of the present invention is not limited to any particular rubber included or excluded above in this invention.

Furthermore, it has also been discovered that in order to increase the bond between the rubber and the reinforcing fillers, the rubber polymer (s) can be functionalized with different groups. These groups can be introduced during polymer initiation as well as termination, and accordingly it is known to provide functionalized polymers at one or both ends of the polymer chain. Examples of functionalized rubber polymers and their related processes are the subject of various United States patents owned by the assignee of registration, such as United States Patent Nos. 5,866,650 and 5,659,065, the content of which is incorporated into this invention. as reference. It is also known to provide functional groups along the polymer chain. In the practice of the present invention, the use of any of the functionalized polymers given above is preferred, but not required.

For example, when mineral fillers are used, in addition to silica and / or carbon black, it is preferred that the polymer contains a silane functionality, such as terminal residual silylethoxy or methylsilylphenoxy groups obtained through the use of a tetraethoxysilane or methyltriphenoxysilane terminator. .

Elastomeric polymers can be used as 100 parts of the rubber in the tread part compound or, they can be combined with any conventionally used tread part including natural rubber, synthetic rubber and combinations thereof. Such rubbers are well known to those skilled in the art and include synthetic polyisoprene rubber, styrene / butadiene rubber (SBR), including SBR emulsion, polybutadiene, butyl rubber, neoprene, ethylene / propylene rubber, ethylene / propylene / diene (EPDM), styrene isoprene butadiene rubber (SIB), acrylonitrile / butadiene rubber (NBR), silicone rubber, fluoroelastomers, ethylene acrylic rubber, ethylene vinyl acetate copolymer (EVA), epichlorohydrin rubbers, chlorinated polyethylene rubbers, chlorosulfonated polyethylene rubbers, hydrogenated nitrile rubber, tetrafluoroethylene / propylene rubber, and the like. When the functionalized polymers are combined with conventional rubbers, the amounts can vary widely within a range comprising 5 to 99 percent by weight of the total rubber, with the conventional rubber (s) closing the balance of the total rubber (100 parts). It is to be appreciated that the minimum amount will depend primarily on the degree of reduced hysteresis that is desired.

Reinforcing fillers can be used in the tread composition in amounts ranging from 5 to 100 parts by weight, per 100 parts by weight of elastomer (phr). Generally, there are two preferred types of reinforcing fillers, carbon black and silica, and these fillers can be used separately within the tread piece composition or in combination with the rest. These fillers are low hysteresis fillers. Although other reinforcing fillers known in the art can be used in the present invention, their utility and interrelationship with the electrically conductive additives described in this invention do not affect the essential nature of the invention. Silica is used in the amount of 1 part to 100 parts by weight per 100 parts of rubber polymer (phr), preferably in an amount of 5 to 80 phr, and most preferably, in an amount of 5 to 30 phr. The usual upper range may be limited by the high viscosity facilitated by fillers of this type. Some of the commercially available silicas that can be used include: Hi-Sil® 215, Hi-Sil® 233 and Hi-Sil® 190, manufactured by PPG Industries. A number of customary commercial grades of different silicas are also available from De Gussa Corporation, Rhone Poulenc, and JM Huber Corporation.

In a preferred embodiment amorphous silica (silicon dioxide) is used as a filler for the composition of the tread piece containing diene polymeric or copolymeric elastomer. Silica are generally of the type of hydrated silicas in a wet process since they are produced by a chemical reaction in water, from which they precipitate as ultrafine spherical particles. These primary particles are strongly associated in aggregates, which instead combine less strongly in agglomerates. The surface area, as measured by the BET procedure, gives the best measure of the reinforcing character of the various silicas. For the silicas of interest for the present invention, the surface area should preferably range from 32 to 400 µm²/ g, being more preferred

ES 2 228 526 T3 100 to 200 m interval²/ g, and the interval being 150 to 220 m²/ g most preferred. The pH of the silica filler is generally 5.5 to 7 or slightly higher, preferably 5.5 to 6.8.

Although the vulcanizable elastomeric tread compounds of the present invention are primarily loaded with silica, the polymers can optionally be compounded with all forms of carbon black, in amounts ranging from 0 to 80 parts by weight. , per 100 parts of rubber (phr), with 1 to 40 phr being preferred. When carbon black is present, with silica, the amount of silica can decrease to about 1 phr, on the other hand it is also present alone at least 5 phr. Similarly, when both silica and carbon black are present, the amount of carbon black can be as low as about one phr or less, but enough silica should be present so that at least about 5 phr of reinforcement loads.

As is known to those skilled in the art, elastomeric compounds as described in this invention are typically charged to a volume fraction of 5 to 25 percent, which is the total volume of the filler (s). ) added divided by the total volume of the elastomeric part. Accordingly, although the minimum amounts expressed in this invention are operable, a usual and preferred range of reinforcing fillers, ie, silica and carbon black, is 30 to 100 phr.

Carbon blacks can include any of the commonly available commercially produced carbon blacks, but those having a surface area (EMSA) of at least 20 µm are preferred.²/ g and more preferably at least 35 m²/ g up to 200 m²/ g or higher. The surface area values ​​used in this application are those determined according to the ASTM D-1765 test using the cetyltrimethyl ammonium bromide (CTAB) technique. Common carbon blacks include baked black, tunnel black, and carbon black. More specifically, examples of carbon blacks include Super Abrasion Baked Blacks (SAF), High Abrasion Baked Blacks (hAf), Rapid Extrusion Baked Blacks (FIF), Fine Baked Blacks (FF), Black Intermediate Super Abrasion Baked (ISAF), Semi-Reinforced Baked Black (SRF), Medium Tunnel Blacks, Hard Process Tunnel Blacks, and Conduit Tunnel Blacks. Other carbon blacks that can be used include acetylene blacks. Mixtures of two or more of the above blacks can be used in the preparation of the carbon black products of the invention. Typical values ​​for the surface areas of common carbon blacks are summarized in TABLE I below:

<td colspan="2">TABLE I</td>

<td colspan="2">CHARCOAL BLACKS</td>

<td>ASTM designation</td><td>Superficial area</td>

<td>(D-1765-82a)</td><td>(m²/ g) (D-3765)</td>

<td>N-110</td><td> 126</td>

<td>N-120</td><td> 111</td>

<td>N-339</td><td> 95</td>

<td>N-330</td><td> 83</td>

<td>N-351</td><td> 74</td>

<td>N-550</td><td> 42</td>

<td>N-660</td><td> 35</td>

The carbon blacks used in the preparation of the elastomeric compositions of the present invention may be in the form of a tablet or in the flocculating mass, not as tablets. Preferably, for more uniform mixing, non-pelletized carbon black is preferred.

Particularly useful is FEF (Rapid Extrusion Furnace) black, a carbon black of relatively large structure and large particle size, namely 40 mm, 40 μm²/ g, of particle size and surface area respectively. Other descriptions of such carbon blacks are found in the literature. See, for example, The Vanderbilt Rubber Handbook, pages 408-424, RT Vanderbilt Co, Norwalk, CT 06855 (1979) and Rubber Technology, Second Edition, pages 51-59, Van Nostrand Reinhold Corporation (1973).

As noted earlier in this invention, one or more additives are included in the tire tread composition to provide improved electrical conductivity to the tire. These polymeric additives are poly (alkylene oxide) containing polymers that have an alkali metal salt dissolved therein. By the term "dissolved" it is meant that the salt has been essentially uniformly dispersed throughout the polymer and is no longer in crystalline form.

ES 2 228 526 T3

Essentially any polyalkylene oxide / alkali metal salt polymer could be used in the present invention. More particularly, the additive is a blended polymer containing polyalkylene oxide side chains impregnated with the alkali metal salt. These additives are added to the tire tread composition in relatively small amounts of 0.1 to 15 parts by weight, per 100 parts of rubber (phr) and preferably have a number average molecular weight of at least about 100,000, and more preferably, at least about 1,000,000. It will be appreciated that although ionically conductive blended polymers impregnated with the metal salts have been used in the past as an electrolyte polymer solution in batteries and the like, these materials have not hitherto been compounded or used in tire tread formulations. to generate a modified rubber part with higher electrical conductivity.

Preferred alkali metal salts include lithium salts. Lithium tetrafluoroborate (LiBF₄) and lithium chloride (LiCl). It will be appreciated that the molar ratio of cations (e.g. Li +) of the salt used to alkylene oxide monomers used as described above is preferably 0.01 to 0.2, and more preferably 0.05 to 0.07. Although essentially any poly (alkylene oxide) containing polymer, together with the alkali metal salt, can be used to form the required electrically conductive additive in accordance with the concepts of the present invention, preferred polymers include either copolymers of poly ( alkylene oxide) end-blocked by unsaturation (eg vinyl) or graft polymers containing polyalkylene oxide.

The unsaturation end-blocked polyalkylene oxide copolymers preferably include a low molecular weight (i.e., less than about 20,000 MWn) unsaturated poly (alkylene oxide) polymer and a polymer of Compatible high molecular weight (ie, at least about 100,000 MWn) suitable to provide a blended polymer having polyalkylene oxide side chains. The term "end-blocked by unsaturation" is intended to indicate that the polymer has been functionalized with an unsaturation group at one of its ends. Preferred unsaturation groups suitable for use in the polymer include those selected from the group consisting of vinyl, acrylate, methacrylate, and fumarate, to name a few. Most preferred is vinyl end-blocked polyalkylene oxide copolymer.

The other preferred polymers are graft polymers containing polyalkylene oxide. Due to the low molecular weight of many polyalkylene oxide, it has been found that they tend to shed from rubber compositions at concentrations greater than about 4 phr, even when reacted with an alkali metal salt, such as lithium tetrafluoroborate (LiBF4) or lithium chloride (LiCl). In order to overcome this problem, a maleic anhydride-containing polymer can be reacted with the polyalkylene oxide-containing polymer to provide the desired graft polymer.

More particularly, the poly (alkylene oxide) part of the grafted polymer should have a sufficiently low molecular weight to prevent it from crystallizing at the temperatures of use and to prevent degradation of the alkali metal salt. Thus, the poly (alkylene oxide) containing polymer should preferably have a number average molecular weight of between 100 and 20,000, and more preferably 300 to 400, before being reacted with the maleic anhydride containing polymer. Conversely, however, this low molecular weight tends to cause the poly (alkylene oxide) containing polymer to detach from the rubber. Accordingly, a maleic anhydride-containing polymer, preferably having a number average molecular weight of at least 100,000, is preferably reacted prior to any reaction with the poly (alkylene oxide)-containing polymer, presenting the reaction product thereof an alkali metal salt (eg lithium) dissolved therein.

The poly (alkylene oxide) containing polymers of the present invention are preferably selected from the group consisting of monohydroxy poly (alkylene oxide) polymers and aziridine end-blocked poly (alkylene oxide) polymers, and more preferably include poly (alkylene oxide), poly (propylene oxide), poly (tetrahydrofuran) and block and random copolymers thereof, and aliphatic and aromatic ether derivatives and fatty acid ester derivatives thereof. When reacting with a polymer containing maleic anhydride, the poly (alkylene oxide) monohydroxy polymers, in combination with polymers containing maleic anhydride, form poly (alkylene oxide) ester-combined polymers in which the poly (alkylene oxide) parts (alkylene oxide) are side chains therein.

The maleic anhydride-containing polymers used can be any of a number of different polymers including poly (alkylvinyl-co-maleic anhydride), poly (styrene-co-maleic anhydride), poly (substituted styrene-maleic anhydride), and poly (a- olefin-co-maleic anhydride). Preferably the maleic anhydride constitutes at least about 10 percent by weight of the maleic anhydride-containing polymer.

The electrically conductive additives of this invention can be synthesized by any means known in the art. Generally, however, the additive can be prepared at a temperature of about 100 ° C on Bradender equipment by mixing a poly (alkylene oxide) / maleic anhydride containing polymer with an alkali metal salt. The part containing the polyalkylene oxide / maleic anhydride preferably includes a polyethylene glycol or polypropylene glycol segment as a homopolyether, a polyether modified organic polyol, and a polyether blocked hydrocarbon polymer or polymers combined with oligo side chains. -oxyalkylene.

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In a preferred embodiment, a poly (methyl vinyl ether-altamaleichydride) -g-poly (ethylene glycol) / lithium tetrafluoroborate methyl ether additive is first synthesized by adding 20 to 30 percent by weight of poly (methyl vinyl ether- alt-maleic anhydride) having a molecular weight of approximately 2,000,000 at a Brabender preheated to approximately 139 ° C. The rotor speed can be set to approximately 80 rpm. After about one minute, 60 to 70 percent by weight of poly (ethylene glycol) monomethyl ether having a molecular weight of about 350 can be added to the Brabender and allowed to mix for another six minutes at 80 rpm or so. After this, 1 to 10 weight percent lithium tetrafluoroborate (Aldrich, 98%) can be added and mixed on the Branbender for another eight minutes at 80 rpm or so to produce the resulting additive, a light brown material. It will be appreciated that the polyalkylene oxide ether is used in excess in order to ensure full use of the lithium salt. In another alternative embodiment, the additive poly (methyl vinyl ether-alt-maleic anhydride) -g-poly (ethylene glycol) / lithium chloride methyl ether can be synthesized by initially preheating the Brabender to about 100 ° C and adding 20 to 30 percent. weight percent poly (methyl vinyl ether-altamaleic hydrochloride) having a number average molecular weight of about 1,130,000. The mixer speed is set back to 80 rpm, and after about 1 minute, 60 to 70 percent by weight of poly (ethylene glycol) methyl ether having a molecular weight of about 350 can be added to the Brabender and allowed to is mixed for another seven minutes or so at 80 rpm before finally adding 1 to 10 percent by weight of lithium chloride and further mixing for another eight minutes or so, the lithium salt dissolving completely in the mixed compound. This material is typically a sticky paste.

Without wishing to be bound by theory, it is believed that the ionically conductive additive, which is a polar compound, binds itself to the charge of silica, which is also polar, through polar-polar interactions, and is therefore believed which generally coats the silica sufficiently to provide electrical conductivity to the tire tread composition.

It will also be appreciated that electrically conductive additives are particularly useful in silica-containing tire tread compositions, although it is believed that the electrical conductivity of well-dispersed carbon black can also be improved. Typically, as in many tires, both silica and carbon black are used. When using silica, it is often usual to add a coupling agent, such as a silane to obtain good physical properties in a cured rubber part containing silica as a filler. Coupling agents are often composed of a silane that has at least a first constituent component, or moiety, (such as a part of silane) capable of reacting with the surface of the silica and, also, an additional moiety capable of interacting with rubber, in particular a sulfur vulcanizable rubber containing carbon-carbon double bonds, or unsaturation. Usually the additional moiety is sulfur in a form of a polysulfide and in particular a polysulfide bridge between said first moieties. In this way, the coupler acts as a connecting bridge between the silica and the rubber and thereby enhances the rubber-reinforcing appearance of the silica. The rubber-reactive group component, namely said additional moiety, of such a coupler may be, for example, one or more of groups such as mercapto, amino, vinyl, epoxy and sulfur groups, preferably a sulfur or mercapto moiety and more preferably sulfur in the form of a polysulfide as a polysulfide bridge between at least two of said first moieties.

Numerous coupling and compatibilizing agents are known for use in the combination of silica and rubber. Particularly useful and preferred silica-based coupling and compatibilizing agents in the present invention include silane coupling and / or compatibilizing agents containing polysulfide components, or structures such as, for example, trialkoxyorganosilane polysulfides, such as, for example, For example, bis (3-trialkoxysilylorgano) polysulfides, containing 2 to 8 sulfur atoms in a polysulfide point, such as, for example, bis (3-triethoxysilylpropyl) tetrasulfide (Si69) and those alkylalkoxysilanes of formula (Ri)₂Yes (OR₂)₂ or R₁Yes (OR₂)₃, in which the alkoxy groups are the same or different; each R₁ independently comprises C₁ to C₁₈aliphatic, C₆ to C₁₂ cyclo-aliphatic oC₆ to C₁₈ aromatics, preferably C₁ to C₁₀ aliphatic, C₆ to C₁₀ cycloaliphatic, or C₆ to C₁₂ aromatics; and each R₂ independently contains one to 6 carbon atoms. Representative examples include octyltriethoxysilane, octyltrimethyloxy silane, (3-glycidoxypropyl) trimethoxysilane, (3-glycidoxypropyl) triethoxysilane, hexyltrimethoxysilane, etiltrimetioxisilano, propyltriethoxysilane, phenyltrimethoxysilane, cyclohexyltrimethoxysilane, ciclohexiltrietioxisilano, dimetildimetioxisilano, 3-chloropropyltriethoxysilane, metacrioltrimetoxisilano, i-butyltriethoxysilane and the like. Of these, bis- (3-triethoxysilylpropyl) (Si69) tetrasulfide is preferred.

The present invention can alternatively use the presence of one or more processing aids with the silica to replace the silane (Si69) to facilitate equal processability of the vulcanizable compound, and less hysteresis of the vulcanized part, without loss of other measured physical properties. . These processing aids include fatty acid esters of C sugars₅ to C₆ hydrogenated and non-hydrogenated, for example sorbitose, mannitose and arabinose. These compounds have at least three hydroxyl groups and one to 3.5 ester groups (sesqui esters). Also useful are polyoxyethylene derivatives thereof. Representative examples include sorbitan oleates, including monooleate, dioleate, trioleate, and sesquioleate, as well as the sorbitan fatty acid esters of laurate, palmitate, and stearate, and polyoxyethylene derivatives thereof.

The filler reinforced elastomeric formulations of the present invention can be vulcanized or cured in a conventional manner with known vulcanizing agents at 0.2 to 5 phr. For example, sulfur or peroxide based curing systems can be used. For a general description of suitable vulcanizing agents reference may be made to Kira-Othmer's Encyclopedia of Chemical Technology, 3rd Edition, Wiley Insterscience,

ES 2 228 526 T3

NY 1982, volume 20, pages 365-468, particularly "Vulcanization Agents and Auxiliary Materials" pages 390-402. The vulcanizing agents can be used alone or in combination.

In the sulfur cure system, when used in compositions of this invention, sulfur is preferably used in amounts of 0.2 phr to 5 phr, with about 1.7 phr being preferred. Furthermore the curing material may provide one or more accelerators or vulcanizing agents including, but not necessarily limited to, dithiocarbamate accelerators, including metal dialkyldithiocarbamates such as, for example, zinc dibutyldithiocarbamate (ZDBDC), zinc diethyldithiocarbamate , zinc dimethyldithiocarbamate and ferric dimethyldithiocarbamate; and thiazole accelerators including 2-mercaptobenzothiazole, the benzothiazole disulfides such as, for example, mercaptobenzothiazole disulfide (MBTS), and the benzothiazole sulfenamides, such as, for example, N-cyclohexyl-2-benzothiazole sulfenamide. Other useful accelerators that can be used with EPDM terpolymers include 2,2'-dibenzothiazyl disulfide, tetramethylthiuram disulfide, 4,4'-dithiomorpholine, dipentamethylenethiuram hexasulfide (DPTH), tetramethylthiuram monosulfide (tetramethylthiuram disulfide, tetramethylthiDSulfide ), N-tert-butyl-2-benzothiasulfenamide (TBBS), zinc 0,0'-dibutylphosphorodithioate, and the like. Specific vulcanization systems may also depend on how the composition is to be used. Furthermore, such systems will depend on the desired vulcanization conditions, eg, vulcanization times, vulcanization temperatures, and vulcanizer pressure.

It will be appreciated that the accelerators listed are not exclusive, and that other vulcanizing agents known in the art can be used to be effective in curing elastomers. For a list of additional vulcanizing agents, see The Vanderbilt Rubber Handbook, RT Vanderbilt Co., Norwalk, Connecticut 06855 (1979).

The tire tread compositions of the present invention can be prepared by compounding or mixing the elastomer with a reinforcing filler such as silica, carbon black, or combinations thereof, the electrically conductive additive and other conventional elastomeric additives. including additional fillers, plasticizers, antioxidants, antiozonants, processing oils, waxes, stearic acid, pigments, and the like, using conventional rubber mixing equipment such as a Brabender preheated to approximately 175 ° C and regrind with some additional carbon black and a silane coupling agent, such as Si69, if necessary, at a slightly lower temperature (approximately 140 ° C). Sulfur or other curing agents can then be added, along with the zinc oxide and any desirable accelerators at a temperature of about 110 ° C and cure at about 165 ° C for about 20 minutes. Although the above process is preferred, it will be understood that any process known in the art suitable for the production of the tire tread compositions of the present invention can be used.

After vulcanization of the load-reinforced composition of the present invention, the composition can be shaped, molded or formed by various procedures well known and readily apparent to those skilled in the manufacture of tires for use in a tire carcass as a tire tread. In particular, the composite tread composition is generally applied to the tire carcass prior to curing and includes a tread pattern. The composite tread is applied to the tire carcass in such a way as to provide a surface to come into contact with the road. The composite tire tread can provide dissipation of electrostatic charges that can accumulate in air tires and the like by passing electrostatic charges through to the road surface. Notably, the tread composition of the present invention maintains its excellent physical properties, while also providing improved snow and ice traction and maintaining excellent wet and dry traction and handling as that of many tread compositions. silica-loaded tire tread. In order to demonstrate the practice of the present invention, the following examples have been prepared and tested as described in the experimentation section described below in this invention. However, the examples should not be construed as limiting the scope of the invention. The claims will serve to define the invention.

Examples

General experimentation

In order to exemplify the practice of the invention, silica filled tread compositions suitable for use in tires were prepared in accordance with the concepts of the present invention and tested for conductivity and physical properties. Tire tread formulations are presented in Table II below:

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<td colspan="7">TABLE. II</td>

<td colspan="3">Silica formulation c</td><td colspan="4">: on conductive polymer</td>

<td>Compound n '</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td>

<td>Rubber styrene butadiene</td><td> 75</td><td> 75</td><td> 75</td><td> 75</td><td> 75</td><td> 75</td>

<td>Natural rubber</td><td> 25</td><td> 25</td><td> 25</td><td> 25</td><td> 25</td><td> 25</td>

<td>Carbon black</td><td> 32</td><td> 32</td><td> 32</td><td> 32</td><td> 32</td><td> 32</td>

<td>Silica</td><td> 30</td><td> 30</td><td> 30</td><td> 30</td><td> 30</td><td> 30</td>

<td>Stearic acid</td><td> 1,5</td><td> 1,5</td><td> 1,5</td><td> 1,5</td><td> 1,5</td><td> 1,5</td>

<td>Wax</td><td> 16,5</td><td> 16,5</td><td> 16,5</td><td> 16,5</td><td> 16,5</td><td> 16,5</td>

<td>Antistatic additive, phr</td><td> 0</td><td> 0,5</td><td> 1</td><td> 2</td><td> 4</td><td> 8</td>

<td colspan="7">TABLE II</td>

<td colspan="3">Silica formulation c</td><td colspan="4">: on conductive polymer</td>

<td>Compound n °</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td>

<td>Carbon Black / Silane Coupling Agent</td><td> 3/3</td><td> 3/3</td><td> 3/3</td><td> 3/3</td><td> 3/3</td><td> 3/3</td>

<td>Zinc oxide</td><td> 2,5</td><td> 2,5</td><td> 2,5</td><td> 2,5</td><td> 2,5</td><td> 2,5</td>

<td>Sulfur</td><td> 1,7</td><td> 1,7</td><td> 1,7</td><td> 1,7</td><td> 1,7</td><td> 1,7</td>

<td>Accelerators</td><td> 2,25</td><td> 2,25</td><td> 2,25</td><td> 2,25</td><td> 2,25</td><td> 2,25</td>

<td>Salt</td><td> --</td><td>LiBF₄</td><td>LiBF,</td><td>LiBF,</td><td>LiBF₄</td><td>LiBF₄</td>

<td>Μ / EO</td><td> __</td><td> 0,054</td><td> 0,054</td><td> 0,054</td><td> 0,054</td><td> 0,054</td>

Specifically, each sample is compounded using a conventional tire tread formulation that included a rubber blend of 75 parts by weight of styrene-butadiene rubber (SBR) and 25 parts by weight of natural rubber. A mixture of about 50/50 carbon black and silica is used as the reinforcing fillers for the composites. Compound # 1 (the control) did not include any electrically conductive additive, while in compound numbers 2-6 different amounts were added ranging from 0.5 to 8 parts by weight of the electrically conductive additive, poly (methyl ether). methyl vinyl ether-alt-maleic anhydride) -g-poly (ethylene glycol) / lithium tetrafluoroborate. This additive was first synthesized by adding approximately 20 grams of poly (methyl vinyl ether-alt-maleic anhydride), available from Aldrich and having a number average molecular weight of approximately 1,130,000, to a Brabender preheated to approximately 139, 8 ° C. The rotor speed was set at approximately 80 rpm. After about one minute, about 48.8 g of the poly (ethylene glycol) monomethyl ether, also available from Aldrich and having a number average molecular weight of about 350, is added to the Brabender and allowed to mix for another six minutes. at 80 rpm. After this, about 5 grams of lithium tetrafluoroborate, LiBF₄ (Aldrich, 98%), and mixed in the Brabender for another eight minutes at 80 rpm to give the resulting additive, a light brown material. The poly (ethylene glycol) monomethyl ether is used in excess to ensure full use of the lithium salt, and the mole ratio of lithium ions to ethylene oxide monomers was calculated to be 0.054.

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The results of the physical and electrical conductivity tests carried out on the compounds described in Table II are provided in Table III.

<td colspan="7">TABLE III</td>

<td colspan="7">Results of the physical test of the silica formulation</td>

<td>Sample no.</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td>

<td colspan="7">Mooney viscosity</td>

<td>ML 1 + 4/130 ° C</td><td> 62,5</td><td> 61,3</td><td> 59,4</td><td> 57,5</td><td> 55,4</td><td> 50,1</td>

<td>T80 (s)</td><td> 8,5</td><td> 8,1</td><td> 8,1</td><td> 7,7</td><td> 7,4</td><td> 7,1</td>

<td colspan="7">Monsanto Cured at 165 ° C</td>

<td>ML (torq)</td><td> 2,64</td><td> 2,74</td><td> 2,68</td><td> 2,51</td><td> 2,47</td><td> 2,14</td>

<td>MH (torq)</td><td> 15,57</td><td> 18,59</td><td> 18,3</td><td> 18,39</td><td> 18,36</td><td> 17,68</td>

<td>Ts2 (min; s)</td><td> 2; 51</td><td> 3; 03</td><td> 3; 19</td><td> 3; 18</td><td> 3; 22</td><td> 2; 38</td>

<td>Tc90 (min; s)</td><td> 11; 01</td><td> 8; 48</td><td> 8; 38</td><td> 7; 54</td><td> 7; 53</td><td> 6; 46</td>

<td>Tan δ to MH</td><td> 0,109</td><td> 0,122</td><td> 0,128</td><td> 0,113</td><td> 0,104</td><td> 0,092</td>

<td>Weather at 175 ° F in MB, min</td><td> 5</td><td> 4</td><td> 4</td><td> 3,75</td><td> 3,75</td><td> 3,83</td>

<td colspan="7">Traction on the ring at 24 ° C</td>

<td>50% modulus, psi</td><td> 219</td><td> 231</td><td> 230</td><td> 229</td><td> 231</td><td> 218</td>

<td>100% modulus, psi</td><td> 431</td><td> 453</td><td> 455</td><td> 454</td><td> 456</td><td> 426</td>

<td>200% modulus,</td><td> 1076</td><td> 1114</td><td> 1122</td><td> 1126</td><td> 1098</td><td> 1026</td>

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<td>psi</td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>300% modulus, psi</td><td> 1965</td><td> 2000</td><td> 2012</td><td> 2020</td><td> 1941</td><td> 1812</td>

<td>Tensile strength, psi</td><td> 3144</td><td> 2982</td><td> 2832</td><td> 2958</td><td> 2844</td><td> 2831</td>

<td>Elongation in%</td><td> 429</td><td> 408</td><td> 390</td><td> 404</td><td> 405</td><td> 425</td>

<td>Break energy, in Ibs / inch³</td><td> 5807</td><td> 5255</td><td> 4789</td><td> 5167</td><td> 5048</td><td> 5273</td>

<td colspan="7">Traction on ring 100 ° C</td>

<td>50% modulus, psi</td><td> 180</td><td> 180</td><td> 183</td><td> 186</td><td> 178</td><td> 183</td>

<td>100% modulus, psi</td><td> 356</td><td> 364</td><td> 371</td><td> 370</td><td> 356</td><td> 360</td>

<td>200% modulus, psi</td><td> 888</td><td> 920</td><td> 921</td><td> 930</td><td> 885</td><td> 882</td>

<td>Tensile strength, psi</td><td> 1504</td><td> 1394</td><td> 1272</td><td> 1433</td><td> 1254</td><td> 1530</td>

<td>Elongation in%</td><td> 287</td><td> 267</td><td> 248</td><td> 272</td><td> 257</td><td> 302</td>

<td>Break energy, in lbs / in³</td><td> 1822</td><td> 1579</td><td> 1373</td><td> 1683</td><td> 1389</td><td> 2054</td>

<td>Tear of the ring at 171 ° C, ppi</td><td> 111</td><td> 113</td><td> 102</td><td> 109</td><td> 90,9</td><td> 99, 9</td>

<td colspan="7">TABLE III</td>

<td colspan="7">Results of the physical test of the silica formulation</td>

<td>Sample no.</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td>

<td>Pendulum shock elasticity at 24 ° C</td><td> 42,8</td><td> 42</td><td> 42,2</td><td> 42</td><td> 41,6</td><td> 42,8</td>

<td>Pendulum shock elasticity at 65 ° C</td><td> 53,2</td><td> 54,2</td><td> 54,8</td><td> 54,4</td><td> 54,2</td><td> 54,8</td>

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<td>New Lamboum a 65%, g lost</td><td> 0,1409</td><td> 0,1474</td><td> 0,1477</td><td> 0,1349</td><td> 0,1394</td><td> 0,148</td>

<td>New Lamboum a 65%, INDEX</td><td> 1, 00</td><td> 0,96</td><td> 0, 95</td><td> 1,04</td><td> 1,01</td><td> 0, 95</td>

<td>Wet stanley London (# / std)</td><td> 56</td><td> 58</td><td> 56</td><td> 59</td><td> 57</td><td> 58</td>

<td>Shore A hardness, at temp. environment (peak)</td><td> 69</td><td> 70,7</td><td> 70,1</td><td> 68,9</td><td> 71,1</td><td> 69,5</td>

<td>index of dispersion # 1, %</td><td> 88,4</td><td> 94,7</td><td> 85,7</td><td> 93,7</td><td> 96,5</td><td> 88</td>

<td colspan="7">Geometric properties at 3.14 rad / s</td>

<td>Tan δ at 7% elongation at 24 ° C</td><td> 0,177</td><td> 0,1734</td><td> 0,1705</td><td> 0,1775</td><td> 0,171</td><td> 0,1679</td>

<td>G (MPa) at 7% elongation at 24 ° C</td><td> 0,616</td><td> 0,611</td><td> 0,648</td><td> 0,653</td><td> 0,618</td><td> 0,627</td>

<td>AG¹ (Mpa) to 24 ° C</td><td> 4,059</td><td> 3,773</td><td> 4,075</td><td> 4,119</td><td> 3,647</td><td> 3,734</td>

<td>G¹ (Mpa) at elongation at 14.5% at 24 ° C</td><td> 2,72</td><td> 2,838</td><td> 3,064</td><td> 2,985</td><td> 2,919</td><td> 2,99</td>

<td>Tan δ at 7% elongation at 65 ° C</td><td> 0,125</td><td> 0,1221</td><td> 0,1214</td><td> 0,1221</td><td> 0,1168</td><td> 0,1181</td>

<td>G (MPa) at 7% elongation at 65 ° C</td><td> 0,361</td><td> 0,348</td><td> 0,364</td><td> 0,357</td><td> 0,341</td><td> 0,348</td>

<td>AG¹ (Mpa) to 65 ° C</td><td> 2,338</td><td> 2,44</td><td> 2,616</td><td> 2,432</td><td> 2,335</td><td> 2,403</td>

<td>G '(MPa) at elongation of 14.5% at 65 ° C</td><td> 2,435</td><td> 2,454</td><td> 2,556</td><td> 2,511</td><td> 2,507</td><td> 2,465</td>

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<td colspan="7">Volume resistivity model 803B Test on 0.1 '' sheet</td>

<td>Electrical resistance, ohm</td><td>l, 40E + 09</td><td>4.70E + 08</td><td>3.00E + 08</td><td>3.50E + 08</td><td>100E + 0 8</td><td>2.10E + 07</td>

<td>Average thickness, inches</td><td> 0,106</td><td> 0,109</td><td> 0,106</td><td> 0,108</td><td> 0,110</td><td> 0,107</td>

<td>Resistivity</td><td>3.24E +</td><td>1.05E +</td><td>6.94E +</td><td>7.91E +</td><td>2.22E +</td><td>4.79E +</td>

<td>volumetric, ohm-cm</td><td> 10</td><td> 10</td><td> 09</td><td> 09</td><td> 09</td><td> 08</td>

Based on the results of tests carried out, as indicated in Table III, it will be appreciated that the silica-filled tire tread formulations of the present invention containing a polyalkylene oxide ester compound which exhibiting a hygroscopic salt dissolved therein showed improved electrical conductivity by approximately two orders of magnitude for samples of similar thickness. The conductivity of the samples can be determined as the reciprocal value of the volume resistivity as shown in Table III (1 / ohm-cm). After an analysis of the rheometric results, it is clear that the addition of the additive provided a better dispersion of the silica and carbon black in the composite samples, while maintaining essentially the same physical characteristics regarding viscosity, modulus and Shore A hardness than the compound (# 1) that did not include any electrically conductive additive.

In conclusion, it should be clear from the foregoing tests and specification that a tire having a composite tread structure of the type described in this invention effectively dissipates electrostatic charges that can be generated in a tire, at the same time. At the same time, it improves the performance and traction in wet and dry as well as the performance of the tire and also reduces hysteresis.

Thus, it should be apparent that the composite tread of the present invention is highly effective in dissipating electrostatic charge or preventing it from accumulating in tires. The invention is particularly suitable for use on air, radial and bias tires, but is not necessarily limited thereto. Based on the above description it should now be apparent that the use of the composite tread structure described in this invention will accomplish the objects indicated above. It is therefore to be understood that any apparent variation will be within the scope of the claimed invention and therefore, the selection of specific component elements can be determined without departing from the spirit of the invention discussed and described herein. In particular, the rubber compositions of the present invention are not necessarily limited to those indicated above. They can be substituted by other rubber compositions that have physical properties similar to those described above.