CA2243091A1

CA2243091A1 - Improved processability of silica-filled rubber stocks

Info

Publication number: CA2243091A1
Application number: CA002243091A
Authority: CA
Inventors: Ashley S. Hilton; William M. Cole; William L. Hergenrother
Original assignee: Ashley S. Hilton; William M. Cole; William L. Hergenrother; Bridgestone Corporation
Current assignee: Bridgestone Corp
Priority date: 1997-07-11
Filing date: 1998-07-10
Publication date: 1999-01-11
Also published as: ES2193443T3; EP0890606B1; DE69811436T2; EP0890606A1; US20020026001A1; DE69811436D1; US6384118B1; JPH11130874A; US6348531B1; US6221943B1

Abstract

A processable rubber stock is produced by the preparation of a silica-filled, vulcanized elastomeric compound comprising mixing an elastomer with an amorphoussilica filler, from 0 to less than about 1% by weight based on said silica filler of bis[3-(triethoxysilyl)propyl]tetrasulfide, an alkylalkoxysilane and a cure agent. A further processing aid comprising at least one of an ester of a fatty acid or an ester of a polyol is preferred. The elastomer is preferably a diene monomer homopolymer or a copolymer of at least one diene and at least one monovinyl aromatic monomer. By effecting vulcanization, a vulcanized elastomeric compound is produced containing good physical properties for use as tread stock for a pneumatic tire.

Description

. CA 02243091 1998-07-10 ~9153 - 1-IMPROVED PROCESSABILlT~ OF SILICA-FILLED
RUBBER STOCKS

TECI~NICAL ~lELD
The subject invention relates to the p,ocessing and vulcanization of diene polymer and copolymer elastomer containing rubber stocks. More specifically, thepresent invention relates to the proces~ing and vulcanization of diene polymer and copolymer elastomer-con~ining. silica-filled rubber stocks using a mixture of silanes as processing aids.
BACKGROUND OF THE INVENTION
In the art it is desirable to pro.luce elastomeric compounds exhibiting reduced hysteresis when properly compounded with other ingredients such as reinforcing agents, followed by vulcanization. Such elastomers, when compounded, fabricated and vulcanized into components for constructing articles such as tires, power belts, and the like, will manifest properties of increased lebound, dec,eased rolling resistance and less heat-build up when subjected to mech~nir~l stress during normal use.
The hysteresis of an elastomer refers to the difference be-lwe~ll the energy applied to deform an article made from the elastomer and the energy released as the elastomer returns to its initial, undeformed state. In pneumatic tires, lowered hysteresis prope,Lies are associated with reduced rolling resistance and heat build-up during operation of the tire. These prope.lies, in turn, result in lowered fuel con~ tion of vehicles using such tires.
In such contexts, the propel ty of lowered hysteresis of compounded, vulcanizable elastomer compositions is particularly significant. Examples of such compounded elastomer systems are known to the art and are con".,ised of at least one elastomer (that is, a natural or synthetic polymer exhibiting elastomeric plope"ies, such as a rubber), a reinforcing filler agent (such as finely divided carbon ~olack, thermal black, or mineral fillers such as clay and the like) and a vulc~ni7.ing system such as sulfur-containing vulcanizing (that is, curing) system.
Previous attempts at preparing readily processable, vulcanizable, silica-filled rubber stocks containing natural rubber or diene polymer and copolymer ela~,lu.nc.~ have focused upon the sequence of adding ingredients during mixing (Bomal, et al., Influence of Mixing procedures on t/re Proper~ies of a SilicQ Rernforced Agncul~ural nre ~re~ld, May 1992), the addition of de-agglomeration agents such as zinc methacrylate and zinc octoate, or SBR-silica coupling agents such as l,ler~plo propyl trimethoxy silane 5 (f~ewitt, Processing ~cchnology of Silic~ R~;n~orced SBR, Elastomencs, pp 33-37, March 1981), and the use of bis[3-(triethoxysilyl)propyl~tetrasulfide (Si69) pluCeSSh~g aid (Degussa, PP(~).
The use of Si69 processing aid in the forrnulation of silica-filled rubber stocks has been successful, but generally requires a large amount of the additive, such 10 as 10% by weight based on the weight of silica, in order to be effective.
Precipitated silica has been increasingly used as a reinforcing particulate filler in carbon black-filled rubber co,~ one-~ts of tires and mechanical goods. Silica-loaded rubber stocks, however, exhibit relatively poor processability.
The present invention provides a mixture of silanes for use as processing aids 15 for silica-filled rubber stocks, which greatly improve the processability and properties of the forrnulations and resulting vulcanized product.

SUMMARY OF INVENTION
It is therefore an object of the present invention to provide rubber stock 20 processing aids which improve the processability of formulations of diene polymer elastomers with silica-filler.
It is another object of the present invention to provide a method for reducing the viscosity of silica-filled elastomeric vulcanizable coillpou,lds.
It is another object of the present inYention to provide a metho(l ~or 25 enhancing the processability of silica-filled elastomeric vulcanizable co~"poullds.
It is another object of the present invention to provide vulcanizable silica-filled elastomeric compounds having enhance~ physical prope.lies.
The foregoing objects, together with the advantages thereof over the existing art, which shall become appare"l from the specification which follows, are accomplished 30 by the invention as hereinafter described and claimed.
The present invention provides a process for the prepa. ation of a silica-filled.
vulcanized elastomeric co,..pou"d co".~),ising: mixing an elastomer with an amorphous silica filler, from 0 to less than about 1~ by weight based on said silica filler of bis~3-~ 9153 - 3 --(triethoxysilyl)propyl~tetrasulfide, an alkylalkoxysilane and a cure agent; and, effecling vulcanization. Preferably, the elastomer is a diene monomer homopolymer or a copolymer of a diene monomer and a monovinyl aromalic monomer.
The present invention further provides a vulcanizable silica-filled co~ ound comprising an elastomer, a silica filler, from 0 to less than about 1% by weight based on said silica filler of bis[3-(triethoxysilyl)propyl]tetrasulfide (Si69), an alkylalkoxysilane and a cure agent. Preferably, the elastomer is styrene butadiene rubber, optionally con~aining a carbon black filler. The compoulld is more readily processable during mixing, due to the use of the mixture of silane processing aids.
10The present invention further provides a pneul--~.lic tire compri~ing tread stock vulcanized from the inventive vulcanizable silica-filled co..,L,ound.

DETAILED DESCRIlYrION OF THE PREF~RRED EMBODIMENTS
In general, the present invention provides a means to reduce the level of Si69 15needed to obtain good physical properties in a cured rubber stock con~aining silica as a filler. In addition, the present invention further provides ma;.,lenallee of the processability of the compounded stock, as measured by Mooney viscosity, at the same level as achieved with high levels of Si69.
The present invention utilizes the presence of an alkylalkoxysilane as a silica 20hydrophobating agent, such that minimal amounts of Si6g ate needed to obtain good processability, and yet still give good physical p~ ,ellies. According to the invention, therefore, a less costly silane can be substituted for lhe majority or all of the Si69 that would be normally used without any loss of processability or pro~ ies. Additionally, remilling can be eliminated, and the cure of the rubber stock is not dependent on the 2Shigh sulfur level present in the Si69.
The silica-hydrol~hobating agenls useful according to the present invention include those alkylalkoxysilanes of the forrnula (R1)2Si(OR2)2 or R1Si(OR2)3, wherein the alkoxy groups are the same or are different; each R1 independently col.l,isillg C1 to about C18 aliphatic, about C6 to about C12 cyclo-aliphatic, or about C6 to about C18 30aromatic, preferably Cl to about C10 aliphatic, about C6 to about C10 cyclo-aliphatic.
or about C6 to about C12 aromatic; and each R2 independently con~aining from one to about 6 carbon atoms. Repr~ a~i~e examples include octyltriethoxy silane, octyltrimethyloxy si!ane, (3-glycidoxypropyl)trimethoxy silane, (3-9~53 -4 -glycidoxypropyl)triethoxy silane, hexyltrimethoxy silane, ethyltri~ hyoxy silane, propyltriethoxy 5ilane, phenyltrimethoxy silane, cyclohe~ylll ill-~lhoxy silane,cyclohexyltriethyoxy silane, dimethyldimcthyoxy silane, 3-chl~to~rol,yllriethoxy silane, methacryoltrimethoxy silane, i-butyltriethoxy silane, and the like. Of these, 5 octyltriethoxysilane is preferred.
According to the present invention, polymerized elastomet is col"~,ounded in the rubber stock, e.g., polybutadiene, polyisople.le and the like, and copolymers thereof with monovinyl aromatics such as styrene, alpha methyl styrene and the like, or trienes such as myrcene. Thus, the elastomers include diene homopolymers, A, and10 copolymers thereof with monovinyl aromatic polymers, B. Exemplary diene homopolymers are those prepared from diolefin monomers having from 4 to about 12carbon atoms. Exemplary vinyl aromatic polymers are those plel,aled from monomers having from 8 to about 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 include styrene, o~-methylstyrene, p-methylstyrene, vinyltoluenes and vinylnaphthalenes. The conjugated diene monomer and aromatic vinyl monomer are normally used at the weight ratios of about 90:10 to about 55:45, preferably about 80:20 to about 6S:35.
Preferred elastomers include diene homopolymers such as polybutadiene and 20 polyisople~lc and copolymers such as styrene butadiene rubber (SBR). Copolymers can comprise from about 99 to 20 percent by weight of diene units and from about 1 to about 80 percent by weight of monovinyl aromatic or triene units, totaling 100 percent.
The polymers and copolymers of the present invention may have the diene portion with a 1,2-microstructure contents ranging from about 10 to about 80 percent, with ~he 25 preferred polymers or copolymers having 1,2-microstructure contents of from about 25 to 65 percent. The molecular weight of the polymer that is produced according to the present invention, is preferably such that a proton-quenched sample will exhibit a gum Mooney viscosity (ML4/212~F) of from about 2 to about 150. The copolymers are preferably random copolymers which result from simullaneous copoly,lle.i~ation of the 30 mononl~,s, as is known in the art. Also included are nonfunctionalized cis-polybutadiene, ethylene-propylene-diene n~ono.,lcl (EPDM), emulsion SBR and natural rubber.

~9153 - 5 -Initiators known in the art such as an organolithium initiator, preferably an alkyllithium initiator, can be employed to prepare the elastomer. More particularly, the initiators used in the present invention include N-lithio-hexamethyleneimine, organolithium co.,.~)ounds such as n-butyllithium, tributyltin lithium, dialkylaminolithium 5 compounds such as dirnethylarninolithium, di~lhyl~,--inolithium, dipropylaminolithium, dibutylaminolithium and the like, dialkylaminoalkyllithium co---pounds such a diethylaminopropyllithium and the like, and trialkyl stanyl lithium, wherein the alkyl group contains 1 to about 12 carbon atoms, preferably 1 to about 4 carbon atoms.Poly---~liLalion is usually conducted in a conventional solvent for anionic 10 poly..,elizations such as the various cyclic and acyclic hexanes, heptanes, octanes, pentanes, their alkylated derivatives, and mixtures thereof. Other techniques for polymerization, such as semi-batch and cortil-uous polymerization may be employed.
In order to promote randomization in copolymerization and to increase vinyl content, a coordinator may optionally be added to the pol~l,lelization ingredients. Amounts 15 range between 0 to 90 or more equivalcnts per equivalent of lithium. The amount depends upon the amount of vinyl desired, the level of styrene employed and the temperature of the polymerizations, as well as the nature of the specific polar coordinator employed.
Compounds useful as coordinators are organic and include those having an 20 oxygen or nitrogen hetcro-atom and a non-bonded pair of electrons. Examples include dialkyl ethers of mono and oligo alkylene glycols; "crown" ethers; tertiary amines such as tetramethylethylene diamine (TMEDA); THF; T~P oligomers; linear and cyclic oligomeric oxolanyl a~kanes, such as 2-2'-di(tetrahydrofuryl) plor~alle, di-pil-crilJyl ethane,hexamethylphosphoramide,N-N'-dimethylpil c.~ine,diazabicyclooctane,diethyl 25 ether, tributylamine and the like. ~etails of linear and cyclic oligomeric oxolanyl coordinators can be found in U.S. Pat. No. 4,429,091, owned by the Assignee of record, the subject matter of which is h~col~Jolat~ herein by reference.
Pol)ilneliLdtiol1 is usually begun by charging a blend of the l..ono---e.(s) andsolvent to a suitable reactlon vessel, followed by the addition of the coordinator and the 30 initiator solution previously described. Alte.-,ali~ely, the monomer and coordinator can be added to the initiator. The procedure is carried out under anhydrous, anaelol)ic conditions. The reactants are heated to a te.npc.dt~re of from about 10~ to 150~C and I, .
~9153 - 6 -are agitated for about 0.1 to 24 hours. After poly-,le~i~ation is complete, the product is removed from the heat and terminated in one or more ways.
To terminate the pol~l.,e.j~ation, a terminating agent, coupling agent or linking agent may be employed, all of these agents being collectively referred to herein 5 as "terminating agents". Certain of these agents may provide the resulting polymer with a multifunctionality. That is, the polymers initiated according to the present invention, carry at least one amine functional group as discussed hereinabove, and may also carry a second functional group selected and derived from the group consi~li..g of terminating agents, coupling agents and linking agents.
Examples of terminating agents according to the present invention include those commonly employed in the art, including hydrogen, waler, steam, an alcohol such as isoplopdnol, 1,3-dimethyl-2-imidazolidinone (DMI), carbodiimides, N-methylpyrrolidine, cyclic amiaes, cyclic ureas, isocyanates, Schiff bases, 4,4'-bis(diethylamino) benzophenone, and the like. Other useful terminating agents may 15 include those of the structural formula (Rl)a ZXb. wherein Z is tin or silicon. It is preferred that Z is tin. Rl is an alkyl having from about 1 to about 20 carbon atoms;
a cycloalkyl having from about 3 to about 20 carbon atoms; an aryl having from about 6 to about 20 carbon atoms; or, an aralkyl having from about 7 to about 20 carbon atoms. For example, Rl may include methyl, ethyl, n-butyl, neophyl, phenyl, 20 cyclohexyl or the like. X is a halogen, such as chlorine or blu---inc, or an alkoxy (-ORl), "a" is from 0 to 3, and "b" is from about I to 4; where a + b = 4. Examples of such terrninating agents include tin tetrachloride, (Rl)3SnCI, (Rl)2SnC12, RISnCl3, and RlSiC13 as well as methyll-iphel~oxysilane (MeSi(OPh3)).
The terminating agent is addcd to the reaction vessel, and the vessel is 25 agitated for about I to about 1000 minutes. As a result, an elastomer is produced having an even greater amnity for silica compounding materials, and hence, even further reduced hysteresis. Additional examples of terminating agents include lhose found in U.~. Patent No. 4,616,069 which is herein inco.~,o.~ted by reference. It is to be understood that practice of the present invenlion is not limited solely to these 30 terminators inasmuch as other co..lpou,lds that are reactive with the polymer bound lithium moiety can be selected to provide a desired functional group.
Quenching i!~ usually conduc~ed by stirring the polymer and quenching agent for about 0.05 to about 2 hours at temperatures of from about 30~ to 120~ C to ensure ~9153 - 7 -complete reaction. Polymers terminated with a functional group as discussed hereinabove, can be ~ se~uently ~lu~nc}lcd with alcohol or other quenching agents as described hereinabove.
Lastly, the solvent is removed from thc polymer by conventional techniques 5 such as drum drying, extruder drying, vacuum drying or the like, which may be combined with coagulalion with water, alcohol or steam, thermal desolventization, or any other suitable method. If coagulation with water or steam is used, oven drying may be desirable.
The elastomeric polymers can be utilized as 100 parts of the rubber in the 10 treadstock co,l,pound or, they can be blended with any conventionally employed treadstock rubber which includes natural rubber, synthetic rubber and blends thereof.
Such rubbers are well known to those skilled in the art and include synthetic polyisoprene rubber, styrene/butadiene rubber (SBR), polybutadiene, butyl rubber, Neoprene, ethylene/propylene rubber, ethylene/propylene/diene rubber (EPDM), 15 acrylonitrile/butadiene rubber (NBR), silicone rubber, the fluoroelastomers, ethylene acrylic rubber, ethylene vinyl acetate copolymer (EVt~), epichlorohydrin rubbers, chlorinated polyethylene rubbers, chlorosulfonated polyethylene rubbers, hydrogenated nitrile rubber, tetratluoroethylenelpropylene rubber and the like. When the polymers disclJssed hereinabove are blended with conventional rubbers, the .-n~o~ can vary 20 widely with a range comprising about 5 to about 99 percent by weight of the total rubber. It is to be app,cciated that the minimum amount will depend primarily upon the degree of reduced hysteresis that is desired.
According to the present invention, al,,o,l)hous silica (silicon dioxide) is utilized as a filler for the diene polymer or copolymer elastomer-cont~ining vulcanizable 25 compound. Silicas are generally classed as wet-process, hydrated silicas because they are produced by a chemical reaction in water, from which they are precipitated as ultrafine, spherical particles.
These primary particles strongly associate into aggregates, which in turn combine less strongly into agglo,l,e,..tes. The surface area, as measured by the BET
30 method gives the best measure of the reinforcing character of different silicas. For silicas of interest for the present invcntion, the surface area should be about 32 to about 400 m2/g, with the range of about 100 to about 250 m2/g being preferred, and the range ~91~3 -8 -of about 150 to about 220 m2/g being most preferred. The pH of the silica filler is generally about 5.5 to about 7 or slightly over, preferably about 5.5 to about 6.8.
Silica can be employed in the amount of about I part to about 100 parts per 100 parts of polymer (phr), preferably in an amount from about 5 to about 80 phr. The 5 useful upper range is limited by the high viscosity imparted by fillers of this type. Some of the commercially available silicas which may be used include: Hi-Sil~ 215, Hi-Sil~
233, and Hi-Sil~ 190, all produced by PPG InJu~lries. Also, a number of useful commercial grades of different silicas are available from De Gussa Corporation, Rhone Poulenc, and J.M. ~luber Corporation.
The polymers can be con~l)o~nded with all forrns of carbon black in amount ranging from about 2 to about 50 parts by weight, per 100 parts of rubber (phr), with about 5 to about 40 plIr being preferred. The carbon blacks may include any of the commonly available, commercially-produced carbon blacks but those having a surface area (~MSA) of at least 20 m2/gram and more preferably at least 35 m2/gram up to 200 15 m2/gram or higher are preferred. Surface area values used in this application are those deterrnined by ASTM test D-1765 using the cetyltrin..t}~yl-ammonium bromide (CTAB) technique. Among the useful carbon blacks are furnace black, channel blacks and lamp blacks. More specifically, examples of the carbon blacks include super abrasion furnace (SAF) blacks, high abrasion furnace (HAF) blacks, fast extrusion furnace (FEF) blacks, 20 fine furnace (FF~ blacks, intermediate super abrasion furnace (ISAF3 blacks, semi-reinforcing t'urnace (SRF) blacks, medium prucesshlg channel blacks, hard processing channel blacks and conducting channel blacks. Other carbon blacks which may be utilized include acetylene blacks. Mixtures of two or more of the above blacks can be used in p.~l)al ing the carbon black products of the invention. Typical values for surface 2S areas of usable carbon blacks are ~ lllali~ed in the Table ~ hereinbelow.

9153 _ 9 _ TABLE I
Carbon Blacks ASTM DesignationSurface Area (m2/g) (D-1765-82a) (D-3765) The carbon blacks utilized in the preparation of Ihe rubber compounds of the 15 invention may be in pelletized form or an unpelletized flocculent mass. Preferably, for more uniform mixing, unpelletized carbon black is preferred.
The reinforced rubber compounds can be cured in a conventional manner with known vulcanizing agents at about 0.2 to about 5 phr. For example, sulfur or peroxide-based curing systems may be employed. For a general disclosure of suitable 20 vulcanizing agents one can refer to Kirk-Othmer, Encyclopedia of Chemical Technolo~ey, 3rd ed., Wiley Intelsciellce, N.Y. 1982, Vol. 20, pp. 365-468, particularly "Vulcanization Agents and Auxiliary Materials" pp. 390-402. Vulcanizing agents can be used alone or in combination.
Vulcanizable elastomeric compositions of the invention can be prepared by 25 compounding or mixing the elastomeric polymer with silica, optionally carbon black, the silica-hydrophobating agent according to the present invention, a minimal amount of Si69, and other conventional rubber additives including for example, fillers,plasticizers, antioxidants, curing agents and the like, using ~landard rubber mixin equipment and proced~,les.

9~W~91~3 - 10 -GENERAL ~sX~ lMENTAL
In order to demonstrate the p,epardtion and properties of silica-filled, diene elastomer con~ining rubber stocks prepare~ according to the present invention, styrene butadiene rubber (SBR) polymers were ~e~aled and were cG~IlpGunded using th 5 formulations set forth în Tables 11 and 111 below.
Test results for the Control, C-A, using the Si69 processil,g aid only, and Examples 1 - 3, using silane processing aids according to the invention in Formulation A, are reported in Table 11.

~9153 TABLE II
Forrnulation A for the Partial Re~,lace.nent of Si69 and Physical Test Results Material Amount (phr) Example No C-A I 2 3 Oil 20 2020 20 Silica 60 6060 60 Carbon Black 6 6 6 6 Stearic Acid 2 2 2 2 Wax 0.75 0.75 0.75 0.75 Si-69 5.4 0.6 06 0.6 Silane (Type) -- Octyl Methacroyl Dimethyl Trimethoxy Trimethoxy Dimethoxy Silane (Amount) 0 4 71 4 99 3.62 Tackifier 3.5 3 S 3 5 3.5 Antioxidant 0.95 0 95 0.95 0 g5 Sulfur 1.4 1 4 1 4 1.4 Accelerators 2 4 2 4 2 4 2.4 Zinc Oxide 3 3 3 3 20 Physical ~rope~ties MLI+4 ~ 100~C 93.7 84 7 93.3 88.8 Tensile (psi) ~ 23~C 2913 2216 2476 2834 Tensile (psi) ~ 100~C 1239 954 1122 1294 % Elong at break, 23~C 444 603 504 551 % Elong. at break, 100~C 262 407 342 365 Ring Tear (Iblin) ~ 100~C191 198 179 223 Disl,e.sion lndex, % 72.9 76 1 84 84.3 Test results for the Control, C-B, using the Si69 processing aid only, and Exarnples 4 - 7, using silane ~,loces~ing aids aceo,ding to the invention in Formulation B, are reported in Table III.

9~70~9153 - 12 -TABLE Ill Formulation B for the Partial Repl~ce...~.lt of Si69 and Physical Test Results Msteri~l Amount (phr) Example No. C-B 4 5 6 7 BR. 25 25 25 25 25 Oil 41.25 41.25 41.25 41.25 41.25 Silica 80 80 80 80 80 Carbon Black 8 8 8 8 8 Stearic Acid Wax 1.5 1.5 1.5 1.5 1.5 Si-69 7.2 0.8 0.8 0.8 0.8 Silane (Type) -- Propyl 3- Octyl i-Butyl TriethoxyChlorop,opyl Trie~hoxy Triethoxy Triethoxy Silane (Amount) 0 5.5 6.42 7.39 5.88 Tackifier 3 3 3 3 3 Antioxidant 1.17 1.17 1.17 1.17 1.17 Sulfur 2.8 2.8 2.8 2.8 2.8 Accelerators 2.4 2.4 2.4 2.4 2.4 Zinc Oxide 1.7 1.7 1.7 1.7 1.7 94~r70~9153 - 13 -TABLE III CONTINUED

Physicsl Properties MLI+4~ 100~C 64.8 69.2 96.1 53.8 93.9 Tensile (psi) ~ 2497 2268 2566 2400 2513 23~C
Tensile (psi) ~ 1453 1278 1693 1280 1379 100~C
9~ Elong. at break, 487 614 544 612 649 23~C
% Elong. at break, 386 486 487 467 499 100~C
Ring Tear (Ib/in) ~ 190 270 245 262 298 100~C
Dispersion Index, % 93.1 80.5 95.7 87.9 93.3 A series of tests were conducted, in which the Si69 processing aid was omitted and insoluble sulfur was added, while processing Formulation B with 2 phr 20 octyl-triethoxy silane, and 4 phr sorbitan oleate. Test conditions and results are reported for Exa-l-ples 8 -17 and the Control (no added insoluble sulfur), C-C, in Table IV, below.

9~9153 - 14-Y O ~ ~ ~ O ~ ~ Cr' V~
o ~ o X ~ o ~

~ .

~ oo '~ ~ -- ~ ,~, O

go o ~ ~o o c' v~

.
o ~ ~ o ~ ~ o o' oo ;~;
o oo oo o ~ V~ o ~

m o e ~

c U, C ~ ~ ~ ~1 3 3 C c ~ ~ ~ ~n + C X ~ ~3~ 8 8 94~9 153 _ I S _ ~ ~ ~ g ~ ~ o 3 ~ ~ o ~ ~~ ~ ;~; ~ ~ ~ ~

~ o o ~ , o ~ ~ o X

t~ ~ ~ 'n O ~ ~ I_ O ~ _ ~ ~ o ~ o ~ v~

., ~n --~ ~ O ~ X O x o ~ ~

~ ~ ~ t~ ~~ cr ~ ~

x ~ ~ ~

, o ~ u ~ E
C ~ a ~ ~ ~ ~-8 ~ c ~ ~ K
g g ~ a~ m ~;Z ~ ~ ~C a u~ d E~ ~~

1~ CA 02243091 1998-07-10 g~gl~3 - 16 -A further series of tests were conducted, in which Forrnulation B, desc,ibed in Table 111, was processed with added sulfur and a p~oce;,sh~g aid comprising 1.5 phr oc~yl-triethoxy silane, 0.5 phr Si69, and 4 phr soll,it~,l oleate. Test conditions and results are reported for Examples 18 - 22 in Table V, below.

~9153 - 17 -TABLE V
Physical Propcrties of Formulation B with 1.5 phr Octyl-triethoxysilane, 4 phr Sorbitan, 0.5 Si69 and Insoluble Sulfur Ssmple 1~ l9 20 21 22 Insoluble S (phr) 2.8 3.2 3.6 4 4.4 Total S (phr) 4.2 4.6 5 5.4 S.8 Physical Test Results MLI.~ 4/100~C 81.9 83.6 84.2 86.3 80.8 Monsanlo Cure ~ 171 ~C
ML 13.15 13.2 13.15 13.82 12.48 MH 41.84 44.62 44.62 46.58 46.g8 ts2 2:50 2:44 2:43 2:35 2:38 tc90 10:15 10:12 9:12 9:24 8:59 Ring Tensile ~ 24~C
100% Modulus, psi 273 291 326 341 408 300% Modulus, psi 935 994 1112 1158 1452 Tensile str, psi 2323 2183 2112 2012 2497 % Elongalion 582 537 483 461 460 Break Energy,lbslin2 5760 5099 4545 4164 5130 Ring Tensile ~ 100~C
100% Modulus, psi 251 251 287 307 311 300% Modulus, psi 826 798 933 1030 998 Tensile str, psi 1326 1215 1255 1229 1113 % Elongalion 444 428 388 350 329 Break Energy, Ibs/in22720 2439 2306 2069 1800 Ring Tear ~ 171~C, psi 240 230 201 219 206 Pendulum Rebound 65~C 37.2 39 42.8 39.4 42.4 Wel Slanley London (~/sld) 64/53 61/53 64/53 65/53 65153 Shore A, ~ RT 72 71 72 74 73 Specific Gravity 1.195 I.l96 1.197 1.197 1.202 Rhco,.~lli.s ~2' 7~G slrain lan ô &~ 65~C 0.1577 0.1528 0.14440.1384 0.1533 ~ G' ~ 65~C, MPa 6.89 6.798 6.676 6.285 7.789 Tensile Retraction 12.6 12.4 11.1 tO.4 9.7 Mc, ~1 lO~3 ~/mol X~9153 - I 8 -The present invention can thus further utilize the l"csence of an ester of a fatty acid or an ester of a polyol as a plocesshlg aid to replace the silane Si6~ to give equal procesiability of the vulcanizable co"-~und, and better hot tear strength and lower hysteresis of the vulcanized rubber stock, without loss of the other measured 5 physical properties.
The further processing aid, such as the preferred sorbitan oleate, is air stableand does not decompose. The sorbitan oleate is lower in cost and more storage stable than Si69, and when used with a silica filler and a silane terrninated polymer, gives similar reduction of ML4, and tan ~ with an h~lease in tear strength.
The additional processing aids useful according to the present invention include esters of fatty acids or esters of polyols. Rel)resentative examples include the sorbitan oleates, such as sorbitan monooleate, dioleate, trioleate and sesquioleate, as well as sorbitan esters of laurate, palmate and stearate fatty acids, and the polyoxyethylene derivatives of each, and other polyols, including glycols such as 15 polyhydroxy compounds and the like. Of these, sorbitan monooleate is preferred.
It is therefore demonstrated that the present invention provides a means for improving the processability of formulations of diene polymer elastomers with silica-fil1er, reducing the viscosity of silica-filled elastomeric vulcanizable co"~poullds. It is further demonstrated that the present invention provides vulcanizable silica-filled 20 elastomeric compounds having enhanced physical properties.
It should be apl)lcciated that the present invention is not limited to the specific embodiments described above, but includes variations, modifications andequivalent embodiments defined by the following claims.

Claims

1. A process for the preparation of a silica-filled, vulcanized elastomeric compound comprising:
mixing an elastomer with an amorphous silica filler, 0 to less than about 1% by weight based on said silica filler of bis[3-(triethoxysilyl)propyl]tetrasulfide, an alkylalkoxysilane and a cure agent; and, effecting vulcanization.

2. The process as in claim 1 wherein the elastomer is a diene monomer homopolymer or a copolymer of a diene monomer and a monomer selected from the group consisting of monovinyl aromatic monomers and triene monomers.

3. The process as in claim 1 wherein the alkylalkoxysilane is represented by theformula (R1)2Si(OR2)2 or R1Si(OR2)3, wherein each R1 independently is selected from the group consisting of C1 to about C18 aliphatic, about C6 to about C12 cyclo-aliphatic, and about C6 to about C18 aromatic; and, wherein the alkoxy groups are the same or are different, each R2 independently containing from one to about 6 carbon atoms.

4. The process as in claim 1 wherein the alkylalkoxysilane is represented by theformula (R1)2Si(OR2)2 or R1Si(OR2)3, wherein each R1 independently is selected from the group consisting of C1 to about C10 aliphatic, about C6 to about C10 cyclo-aliphatic, and about C6 to about C12 aromatic; and, wherein the alkoxy groups are the same or are different, each R2 independently containing from one to about 6 carbon atoms.

5. The process as in claim 1 wherein the alkylalkoxysilane is selected from the group consisting of octyltriethoxy silane, octyltrimethyloxy silane, (3-glycidoxypropyl)trimethoxy silane, (3-glycidoxypropyl)triethoxy silane, hexyltrimethoxy silane. ethyltrimethyoxy silane, propyltriethoxy silane, phenyltrimethoxy silane, cyclohexyltrimethoxy silane, cyclohexyltriethyoxy silane, dimethyldimethyoxy silane, 3-chloropropyltriethoxy silane, methacroyltrimethoxy silane, and i-butyltriethoxy silane.

6. The process as in claim 1 wherein the alkylalkoxysilane is octyltriethoxysilane.

7. The process as in claim 1, including mixing prior to vulcanizing, a processing aid comprising at least one of an ester of a fatty acid or an ester of a polyol.

8. The process as in claim 7 wherein the processing aid is selected from the group consisting of at least one sorbitan ester of an oleate, laurate, palmate and stearate fatty acids, polyoxyethylene derivatives thereof, at least one ester of a polyhydroxy compound, and mixtures thereof.

9. The process as in claim 7 wherein the processing aid is sorbitan monooleate.

10. The process as in claim 1 wherein the elastomer is styrene butadiene rubber.

11. The process as in claim 1 wherein the elastomer is a copolymer of styrene butadiene rubber and butyl rubber.

12. The process as in claim 1 including mixing the elastomer with carbon black.

13. The process as in claim 1 including mixing insoluble sulfur prior to vulcanizing.

14. A vulcanizable silica-filled compound comprising an elastomer, a silica filler, from 0 to less than about 1% by weight based on said silica filler of bis[3-(triethoxysilyl)propyl]tetrasulfide, an alkylalkoxysilane and a cure agent.

15. The compound as in claim 14 wherein the alkylalkoxysilane is represented by the formula (R1)2Si(OR2)2 or R1Si(OR2)3, wherein each R1 independently is selected from the group consisting of C1 to about C18 aliphatic, about C6 to about C12 cyclo-aliphatic, and about C6 to about C18 aromatic; and, wherein the alkoxy groups are the same or are different, each R2 independently containing from one to about 6 carbon atoms.

16. The compound as in claim 14 wherein the alkylalkoxysilane is represented by the formula (R1)2Si(OR2)2 or R1Si(OR2)3, wherein each R1 independently is selected from the group consisting of C1 to about C10 aliphatic, about C6 to about C10 cyclo-aliphatic, and about C6 to about C12 aromatic; and, wherein the alkoxy groups are the same or are different, each R2 independently containing from one to about 6 carbon atoms.

17. The compound as in claim 14 wherein the alkylalkoxysilane is selected from the group consisting of octyltriethoxy silane, octyltrimethyloxy silane, (3-glycidoxypropyl)trimethoxy silane, (3-glycidoxypropyl)triethoxy silane, hexyltrimethoxy silane, ethyltrimethyoxy silane, propyltriethoxy silane, phenyltrimethoxy silane, cyclohexyltrimethoxy silane, cyclohexyltriethyoxy silane, dimethyldimethyoxy silane, 3-chloropropyltriethoxy silane, methacryoltrimethoxy silane, and i-butyltriethoxy silane.

18. The compound as in claim 14 wherein the alkylalkoxysilane is octyltriethoxysilane.

19. The compound as in claim 14, including a processing aid comprising at least one of an ester of a fatty acid or an ester of a polyol.

20. The compound as in claim 19 wherein the processing aid is selected from the group consisting of at least one sorbitan ester of an oleate, laurate, palmate and stearate fatty acid, their polyoxyethylene derivatives, at least one ester of a polyhydroxy compound, and mixtures thereof.

21. The compound as in claim 19 wherein the processing aid is sorbitan monooleate.

22. The compound of claim 14 wherein the elastomer is a diene monomer homopolymer or a copolymer of at least one diene and at least one monomer selected from the group consisting of monovinyl aromatic monomers and triene monomers.

23. The compound of claim 22 wherein the elastomer is styrene butadiene rubber.

24. The compound as in claim 23 wherein the elastomer is a copolymer of styrene butadiene rubber and butyl rubber.

25. The compound of claim 14 further containing a carbon black filler.

26. The compound of claim 14 further containing a natural rubber.

27. The compound of claim 19 further containing a carbon black filler.

27. The compound of claim 19 further containing a natural rubber.

28. A pneumatic tire comprising tread stock vulcanized from the vulcanizable silica-filled compound of claim 14.

29. A pneumatic tire comprising tread stock vulcanized from the vulcanizable silica-filled compound of claim 19.