AU2002326753A1 - Rubber compositions and method for increasing the mooney scorch value - Google Patents

Description

RUBBER COMPOSITIONS AND METHOD FOR INCREASING THE MOONEY SCORCH VALUE

BACKGROUND OF THE INVENTION

1 . Technical Field

This invention relates generally to rubber compositions and a method

for increasing the mooney scorch value of the rubber compositions. The rubber

compositions are particularly useful for tire tread applications in vehicles, e.g.,

passenger automobiles and trucks.

2. Description of the Related Art

The tire treads of modern tires must meet performance standards which

require a broad range of desirable properties. Generally, tliree types of performance

standards are important in tread compounds. They include good wear resistance, good

traction and low rolling resistance. Major tire manufacturers have developed tire tread

compounds which provide lower rolling resistance for improved fuel economy and

better skid/traction for a safer ride. Thus, rubber compositions suitable for, e.g., tire

treads, should exhibit not only desirable strength and elongation, particularly at high

temperatures, but also good cracking resistance, good abrasion resistance, desirable

skid resistance, low tangent delta values at 60°C and low frequencies for desirable

rolling resistance of the resulting treads. Additionally, a high complex dynamic

modulus is necessary for maneuverability and steering control. A high mooney scorch

value is further needed for processing safety.

Presently, silica has been added to rubber compositions as a filler to

replace some or substantially all of the carbon black fi ller to improve these properties, e.g , lower rolling resistance. Although more costly than carbon black, the advantages of silica include, for example, improved wet traction, low rolling resistance, etc., with reduced fuel consumption. Indeed, as compared to carbon black, there tends to be a lack of, or at least an insufficient degree of, physical and/or chemical bonding

between the silica particles and the rubber to enable the silica to become a reinforcing filler for the rubber thei eby giving less strength to the rubber. Therefore, a silica filler system requires the use of coupling agents.

Coupling agents are typically used to enhance the rubber reinforcement

characteristics of silica by reacting with both the silica surface and the rubber

elastomer molecule. Such coupling agents, for example, may be premixed or pre- reacted with the silica particles or added to the rubber mix during the rubber/silica processing, or mixing, stage. If the coupling agent and silica are added separately to the rubber mix during the rubber/silica processing, or mixing, stage, it is considered that the coupling agent then combines in situ with the silica. A coupling agent is a bi-functional molecule that will react with the silica at one end thereof and cross-link with the rubber at the other end. In this manner, the reinforcement and strength of the rubber, e.g., the toughness, strength,

modulus, tensile and abrasion resistance, are particularly improved. The coupling

agent is believed to cover the surface of the silica particle which then hinders the

silica from agglomerating with other silica particles. By interfering with the

agglomeration process, the dispersion is improved and therefore the wear and fuel consumption are improved. The use of silica in relatively large proportions for improving various tire properties requires the presence of a sufficient amount of a coupling agent. The coupling agent and silica however retard the cure. Therefore, a silica/coupling agent

tread formulation has been found to undesirably slow the cure rate of the rubber. Additionally, by employing high amounts of the coupling agents results in the rubber compositions being more costly since these materials are expensive.

In order to increase the cure rate, secondary accelerators such as, for

example, diphenyl gυanidine (DPG), have been added to the rubber compositions.

However, the use of secondary accelerators, and particularly DPG with polyalkylene

oxides, result in the rubber composition having a lower mooney scorch value during its manufacture thereby resulting in decreased processing time. Problems associated with a decreased processing time include, for example, precured compounds and rough surfaces on extruded parts. Additionally, diphenyl guanidine is typically

employed in high amounts which result in the rubber compositions being more expensive to manufacture since more material must be used.

It would be desirable to provide a rubber composition which has a decreased cure time and a higher mooney scorch value without sacrificing other

physical properties, e.g., tangent delta value. This will allow for better processing of

the rubber composition during its manufacture.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a decreased cure time when forming the rubber compositions herein. It is also an object of the present invention to provide rubber composition possessing a high mooney scorch value.

In keeping with these and other objects of the present invention, the rubber compositions herein comprise (a) a rubber component; (b) a silica filler; (c) a coupling agent; (d) a cure-enhancing amount of a polyalkylene oxide and (e) a thiuram disulfide having a molecular weight of at least about 400.

By employing a cure -enhancing amount of a polyalkylene oxide, lesser

amounts of a coupling agent can be used in forming the rubber compositions resulting in the compositions disclosed herein advantageously possessing a higher cure rate. Accordingly, the delay in cure/vulcanization of rubber observed with the use of silica and coupling agent alone as noted above has been lessened, if not substantively overcome, in many cases by the cure-enhancing amount of the polyalkylene oxides of the present invention. Thus, the polyalkylene oxides herein have been found to

increase the cure rate and, in some instances, to fully recapture any cure slow down presumed to have resulted from the use of the silica with higher amounts of a coupling agent relative to the present invention which employs lower amounts of a coupling agent with a polyalkylene oxide. In this manner, the polyalkylene oxides have

enabled achievement of the silica benefits in full without the prior art disadvantage

while also achieving a greater economical advantage by using less materials of the more expensive coupling agent.

Additionally, by further employing a high molecular weight thiuram disulfide, i.e., a thiuram disulfide having a weight average molecular weight (M_w) of

at least 400, with the polyalkylene oxides, the mooney scorch value of the rubber compositions are increased thereby allowing for better processing of the compositions without sacrificing other physical properties.

The term "phr" is used herein as its art-recognized sense, i.e., as referring to parts of a respective material per one hundred (100) parts by weight of rubber.

The expression "cure-enhancing amount" as applied to the

polyalkylene oxide employed in the rubber compositions of this invention shall be understood to mean an amount when employed with the coupling agent provides a

decreased cure time of the rubber composition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The rubber compositions of this invention contain at least (a) a rubber component; (b) a silica filler; (c) a coupling agent; and (d) a cure-enhancing amount of at least one polyalkylene oxide and (d) a thiuram disulfide having a molecular weight of at least about 400.

The rubber components for use herein are based on highly unsaturated rubbers such as, for example, natural or synthetic rubbers. Representative of the

highly unsaturated polymers that can be employed in the practice of this invention are diene rubbers. Such rubbers will ordinarily possess an iodine number of between

about 20 to about 450, although highly unsaturated rubbers having a higher or a lower

(e.g., of 50-100) iodine number can also be employed. Illustrative of the diene

rubbers that can be utilized are polymers based on conjugated dienes such as, for

example, 1,3-butadiene; 2-methyl-l ,3-butadiene; 1 ,3-pentadiene; 2,3-dimethyl-l,3- butadiene; and the like, as well as copolymers of such conjugated dienes with monomers such as, for example, styrene, alpha-methylstyrene, acetylene, e.g., vinyl acetylene, acrylonitrile, methacrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinyl acetate, and the like. Preferred highly unsaturated rubbers include natural rubber, cis-polyisoprene, polybutadiene,

poly(styrene-butadiene), styrene-isoprene copolymers, isoprene-butadiene

copolymers, styrene-isoprene-butadiene tripolymers, polychloroprene, chloro-

isobutene-isoprene, nitrile-chloroprene, styrene-chloroprene, and poly (acrylonitrile- butadiene). Moreover, mixtures of two or more highly unsaturated rubbers with

elastomers having lesser unsaturation such as EPDM, EPR, butyl or halogenated butyl

rubbers are also within the contemplation of the invention.

The silica may be of any type that is known to be useful in connection with the reinforcing of rubber compositions. Examples of suitable silica fillers include, but are not limited to, silica, precipitated silica, amorphous silica, vitreous

silica, fumed silica, fused silica, synthetic silicates such as aluminum silicates,

alkaline earth metal silicates such as magnesium silicate and calcium silicate, natural silicates such as kaolin and other naturally occurring silicas and the like. Also useful are highly dispersed silicas having, e.g., BET surfaces of from about 5 to about 1000

m²/g and preferably from about 20 to about 400 m²/g and primary particle diameters

of from about 5 to about 500 nm and preferably from about 10 to about 400 nm. These

highly dispersed silicas can be prepared by, for example, precipitation of solutions of

silicates or by flame hydrolysis of silicon halides. The silicas can also be present in the form of mixed oxides with other metal oxides such as, for example, Al, Mg, Ca, Ba, Zn, Zr, Ti oxides and the like. Commercially available silica fillers known to one skilled in the art include, e.g., those available from such sources as Cabot Corporation under the Cab-O-Sil^® tradename; PPG Industries under the Hi-Sil and Ccptane tradenames; Rhodia under the Zeosil tradename and Degussa AG under the Ultrasil

and Coupsil tradenames. Mixtures of two or more silica fillers can be used in preparing the rubber composition of this invention. A preferred silica for use herein is

Zeosil 1 165MP manufactured by Rhodia.

The silica filler is incorporated into the rubber composition in amounts that can vary widely. Generally, the amount of silica filler can range from about 5 to

about 150 phr, preferably from about 15 to about 100 phr and more preferably from about 30 to about 90 phr.

If desired, carbon black fillers can be employed with the silica filler in forming the rubber compositions of this invention. Suitable carbon black fillers include any of the commonly available, commercially-produced carbon blacks known

to one skilled in the art. Generally, those having a surface area (EMSA) of at least 20

m²/g and more preferably at least 35 m²/g. up to 200 m²/g or higher are preferred. Surface area values used in this application are those determined by ASTM test D-

3765 using the cetyltrimethyl-ammoniυ 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 (SAP)

blacks, high abrasion furnace (HAF) blacks, fast extrusion fumace (FEF) blacks, fine

furnace (FF) blacks, intermediate super abrasion fumace (ISAF) blacks, semi- reinforcing furnace (SRF) blacks, medium processing 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 preparing the rubber compositions of the invention. Typical values for surface areas of usable carbon blacks are summarized in the following Table I. TABLE I

Carbon Blacks

ASTM Surface Area

Designation (m²/g)

(D-1765-82a) (D-3765)

N-1 10 126

N-234 120

N-220 1 1 1

N-339 95

N-330 83

N-550 42

N-660 35

The carbon blacks utilized in the invention may be in pelletized form or an unpelletized flocculant mass. Preferably, for ease of handling, pelletized carbon black is preferred. The carbon blacks, if any, are ordinarily incorporated into the

rubber composition in amounts ranging from about 1 to about 80 phr and preferably from about 5 to about 50 phr.

In compounding a silica filled rubber composition of the present

invention, it is advantageous to employ a coupling agent. Such coupling agents, for example, may be premixed, or pre-reacted, with the silica particles or added to the

rubber mix during the rubber/silica processing, or mixing, stage. If the coupling agent and silica are added separately to the rubber mix during the rubber/silica mixing, or processing stage, it is considered that the coupling agent then combines in situ with

the silica.

In particular, such coupling agents are generally composed of a silane which has a constituent component, or moiety, (the silane portion) capable of reacting with the silica surface and, also, a constituent component, or moiety, capable of reacting with the rubber, e.g., a sulfur vulcanizable rubber which contains

carbon-to-carbon double bonds, or unsaturation. In this manner, then, the coupling agent acts as a connecting bridge between the silica and the rubber thereby enhancing the rubber reinforcement aspect of the silica.

The silane component of the coupling agent apparently forms a bond to the silica surface, possibly through hydrolysis, and the rubber reactive component of

the coupling agent combines with the rubber itself. Generally, the rubber reactive component of the coupling agent is temperature sensitive and tends to combine with the rubber during the final and higher temperature sulfur vulcanization stage, i.e., subsequent to the rubber/silica/coupling mixing stage and after the silane group of the coupling agent has combined with the silica. However, partly because of typical

temperature sensitivity, of the coupling agent, some degree of combination, or

bonding, may occur between the rubber-reactive component of the coupling agent and

the rubber during an initial rubber/silica/coupling agent mixing stage and prior to a

subsequent vulcanization stage. Suitable rubber-reactive group components of the coupling agent include, but are not limited to, one or more of groups such as mercapto, amino, vinyl, epoxy, and sulfur groups. Preferably the rubber-reactive group components of the coupling agent is a sulfur or mercapto moiety with a sulfur group being most preferable.

Examples of a coupling agent for use herein are vinyltrichlorosilane,

vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy) silane, β-

(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ- glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-

methacryloxypropylmethyldimethoxysilane, γ-methacry Ioxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, -β(aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β-(aminoefhyl)γ-

aminopropyltri ethoxysilane, N-β(aminoethyl)γ-aminopropy]triethoxysilane, γ- aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, -phenyl-γ- aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ- ercaptopropyltrimethoxysilane and combinations thereof.

Representative examples of the preferred sulfur-containing coupling

agents are sulfur-containing organosihcon compounds. Specific examples of suitable

sulfur-containing organosihcon compounds are of the following general formula:

Z-R' -S_n-R²-Z in which Z is selected from the group consisting of R³ R³ R⁴

—

wherein R³ is an alkyl group of from 1 to 4 carbon atoms, cyclohexyl or phenyl; and R⁴ is an alkoxy of from 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms; and R¹ and R² are independently a divalent hydrocarbon of from 1 to 18 carbon atoms

and n is an integer of from about 2 to about 8. Specific examples of sulfur-containing organosihcon compounds which may be used herein include, but are not limited to,

3,3'-bis(trimethoxysilylpropyl) disulfide, 3,3'-bis(triethoxysilylpropyl) disulfide,

3,3-bis(triethoxysilylpropyl) tetrasulfide, 3,3'-bis(triethoxysilylpropyl) octasulfide,

3,3'-bis(trimethoxysily]propyl) tetrasulfide, 2,2'-bis(triethoxysiIylethyl) tetrasulfide, 3,3'-bis(trimethoxysilylpropyl) triasulfide, 3,3'-bis(triethoxysilylpropyl) triasulfide,

3,3'-bis(tributoxysilylpropyl) disulfide, 3,3'-bis(trimethoxysilylpropyl) hexasufide, 3,3'-bis(trimethoxysily]propyl) octasulfide, 3,3'-bis(trioctoxysilylpropyl) tetrasulfide,

3,3'-bis(trihexoxysilylpropyl) disulfide, 3,3'-bis(tri-2"-ethylhexoxysilylpropyl)

trisulfide, 3,3'-bis(triisooctoxysilyipropyl) tetrasulfide, 3,3'-bis(tri-t-butoxysilyl-

propyl) disulfide, 2,2'-bis(methoxydiethoxysilylethyl) tetrasulfide,

2,2'-bis(tripropoxysilylethyl) pentasulfide, 3,3'-bis(tricyclohexoxysilylpropyl)

tetrasulfide, 3,3'-bis(tricyclopentoxysilylpropyl) trisulfide, 2,2'-bis(tri-2"-methyl-

cyclohexoxysilylethyl) tetrasulfide, bis(trimethoxysilylmethyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl 3'-diethoxybutoxy-silylpropyltetrasulfide, 2,2'-bis(dimethyl

methoxysilylethyl) disulfide, 2,2'-bis(dimethyl sec.butoxysilylethyl) trisulfide, 3,3'-bis(methylbutylethoxysilylpropyl) tetrasulfide, 3,3'-bis(di t-bυtylmethoxysilylpropyl) tetrasulfide, 2,2'-bis(phenylmethylmethoxysilylethyl) trisulfide, 3,3'-bis(diphenylisopropoxysilylpropyl) tetrasulfide, 3,3'-bis(diphenyl cyclohexoxysilylpropyl) disulfide, 3,3'-bis(dimethylethylmercaptosilylpropyl) tetrasulfide, 2,2'-bis(methyldimethoxysilylethyl) trisulfide, 2,2'-bis(methyl

ethoxypropoxysilylethyl) tetrasulfide, 3,3'-bis(diethylmethoxysilylpropyl) tetrasulfide, 3,3'-bis(ethyl di-sec. butoxysilylpropyl) disulfide, 3,3'-bis(propyldiethoxysilylpropyl)

disulfide, 3,3'-bis(butyl dimethoxysilylpropyl) trisulfide, 3,3'-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenylethoxybutoxysilyl 3'-trimethoxysilyipropyl tetrasulfide, 4,4'-bis(trimethoxysilylbutyl) tetrasulfide,

6,6'-bis(triethoxysilylhexyl) tetrasulfide, 12,12'-bis(triisopiOpoxysilyldodecyl)

disulfide, 18,18'-bis(trimethoxysilyloctadecyl) tetrasulfide, 18,18'-bis(tripropoxysilyl- octadecenyl) tetrasulfide, 4,4'-bis(trimethoxysilyl-butene-2-yl) tetrasulfide, 4,4'-bis(trimethoxysilylcyclohexylene) tetrasulfide, 5,5'-bis(dimethoxymethyl-

silylpentyl) trisulfide, 3,3'-bis(trimethoxysiIyl-2-methylpropyl) tetrasulfide,

3,3'-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide and the like. Preferred coupling agents for use herein are 3,3'-bis(triethoxysilylpropyl) disulfide and 3,3- bis(triethoxysilylpropyl) tetrasulfide.

The polyalkylene oxides used herein advantageously decrease the cure

time of the rubber compositions of this invention when added thereto in a cure-

enhancing amount. Suitable polyalkylene oxides for use herein can be a polyalkylene

oxide which is a polyether of the general formula X(R-O-)_nH where R may be one or more of the following groups: mefhylene, ethylene, propylene or tetramethylene group; n is an integer of from 1 to about 50, preferably from about 2 to about 30 and most preferably from about 4 to about 20; and X is a non-aromatic starter molecule containing 1 to about 12 and preferably 2 to 6 functional groups. Representative of the polyalkylene oxides include, but are not limited to, dimethylene glycol, diethylene glycol, dipropylene glycol, trimethylene glycol, triethylene glycol, tripropylene glycol, polyethylene oxide, polypropylene oxide, polybutylene oxide and the like and

mixtures thereof. A preferred polyalkylene oxide for use herein is diethlyene glycol.

By employing the foregoing polyalkylene oxides herein in a cure- enhancing amount, the amount of coupling agent necessary to compound a silica filled

rubber composition is reduced thereby providing an economical advantage.

Accordingly, amounts of the coupling agent range from about 0.5 to about 10 phr, preferably from about 1 to about 8 phr and most preferably from about 1 5 to about 7 phr while the cure-enhancing amount of the polyalkylene oxide will ordinarily range

from about 0.5 to about 10 preferably from about 1 to about 8 and most preferably from about 1.1 to about 5 phr. The foregoing polyalkylene oxides can be, for

example, premixed, or blended, with the coupling agents or added to the rubber mix during the rubber/silica coupling agent processing, or mixing, stage.

The high molecular weight thiuram disulfides for use in the rubber

composition of this invention as a secondary accelerator advantageously provide a

rubber composition possessing a greater mooney scorch value than that of a similar

rubber composition in which a significant amount up to the entire amount of the thiuram disulfide has been replaced with diphenyl guanidine as an accelerator. The

thiuram disulfides herein will have a weight average molecular weight of at least 400, preferably from about 500 to about 1250 and most preferably from about 800 to about 1000. Representative of these thiuram disulfides are those of the genera] formula

wherein R¹, R², R³ and R⁴ each are the same or different and are hydrocarbons containing, for example, from about 4 to about 30 carbon atoms, optionally containing one or more heterocyclic groups, or R¹ and R² and/or R³ and R⁴ together with the

nitrogen atom to which they are bonded are joined together to form a heterocyclic

group, optionally containing one or more additional heterocyclic atoms. Specific thiuram disulfides include those in which R¹, R², R³ and R⁴ are indepehdently selected to be t-butyl, pentyl, hexyl, cyclohexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, stearyl, oleyl, phenyl, benzyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosanyl, and the like. It is particularly

advantageous to employ a thiuram disulfide wherein R¹, R², R³ and R⁴ each possess between 8 to 18 carbon atoms. A particularly preferred thiuram disulfide for use herein is wherein R¹, R², R³ and R⁴ each possess between 12 and 14 carbon atoms.

Generally, the thiuram disulfide is present in the rubber composition of

this invention in an amount ranging from about 0.10 to about 1.0 phr, preferably from

about 0.15 to about 0.75 phr and most preferably from about 0.20 to about 0.50 phr.

The rubber compositions of this invention can be formulated in any conventional manner. Additionally, at least one other common additive can be added

to the rubber compositions of this invention, if desired or necessary, in a suitable amount. Suitable common additives for use herein include vulcanizing agents,

activators, retarders, antioxidants, plasticizing oils and softeners, fillers other than

silica and carbon black, reinforcing pigments, antiozonants, waxes, tackifier resins,

and the like and combinations thereof.

The rubber compositions of this invention are particularly useful when

manufactured into articles such as, for example, tires, motor mounts, rubber bushings,

power belts, printing rolls, rubber shoe heels and soles, rubber floor tiles, caster

wheels, elastomer seals and gaskets, conveyor belt covers, hard rubber battery cases,

automobile floor mats, mud flap for trucks, ball mill liners, windshield wiper blades

and the like. Preferably, the rubber compositions of this invention are advantageously

used in a tire as a component of any or all of the thermosetting rubber-containing

portions of the tire. These include the tread, sidewall, and carcass portions intended

for, but not exclusive to, a truck tire, passenger tire, off-road vehicle tire, vehicle tire,

high speed tire, and motorcycle tire that also contain many different reinforcing layers

therein. Such rubber or tire tread compositions in accordance with the invention may

be used for the manufacture of tires or for the re-capping of worn tires.

EXAMPLES

The following non-limiting examples are intended to further illustrate

the present invention and are not intended to limit the scope of the invention in any

manner.

COMPARATIVE EXAMPLES A-D AND EXAMPLES 1-3

Employing the ingredients indicated in Tables II and III (λvhich are

listed in parts per hundred of rubber by weight), several rubber compositions were compounded in the following mannei the ingredients indicated in Table II were added to an internal mixer and mixed until the materials are incorporated and thoroughly

dispersed and discharged from the mixer Discharge temperatures of about 160°C are typical The batch is cooled, and is reintroduced into the mixer along with the ingredients indicated m Table III The second pass is shorter and discharge temperatures generally run between 93-105°C

TABLE II - PHASE I

Comp Ex /Ex Λ B C D I 2 3

SOLFLEX 1216' 75 00 75 00 75 00 75 00 75 00 75 00 75 00

BUDENE 1207² 25 00 25 00 25 00 25 00 25 00 25 00 25 00

ZEOSIL I ϊ 65" 44 00 44 00 44 00 44 00 44 00 44 00 44 00

N234" 32 00 32 00 32 00 32 00 32 00 32 00 32 00

SILQUEST A1289⁵ 3 52 1 76 1 76 1 76 1 76 1 76 1 76

DEG (LIQUID) 0 00 1 76 0 00 0 00 1 76 0 00 0 00

DIPROPYLENE

GLYCOL 0 00 0 00 1 76 0 00 0 00 1 76 0 00

TRIETI1YLENE

GLYCOL 0 00 0 00 0 00 1 76 0 00 0 00 1 76

STEAPJC ACID 1 00 1 00 1 00 1 00 1 00 1 00 1 00

FLEXZONE 7P⁶ 2 00 2 00 2 00 2 00 2 00 2 00 2 00

SUNPROOF

IMPROVED 1 50 1 50 1 50 1 50 1 50 1 50 1 50

SUNDEX 8125⁸ 40 00 40 00 40 00 40 00 40 00 40 00 40 00

MB1 TOTAL 224 02 224 02 224 02 224 02 224 02 224 02 224 02

(1) Solution styrene-butadiene rubber low styrene and medium vinyl content available from Goodyear

(2) Polybutadiene rubber available from Goodyear

(3) Highly dispersable silica available from Rhodia

(4) High surface area carbon black available from Cabot Corp

(5) Tetrasulfide coupling agent available fiom OS1 Specialty Chemicals

(6) Paraphenylene diamine available from Uniroyal Chemical Company

(7) Blend of hydrocarbon waxes available from Uniroyal Chemical Company

(8) Aromatic oil available from Sun Oil TABLE HI-PHASE II

Comp Ex /Ex A B C D I 2 3

MB-1⁹ 224 02 224 02 224 02 224 02 224 02 224 02 224 02

Zinc Oxide 2 50 2 50 2 50 2 50 2 50 2 50 2 50

Dela S¹⁰ 1 50 1 50 1 50 1 50 1 50 1 50 1 50

Diphenyl Guanadine 1 00 1 00 1 00 1 00 0 00 0 00 0 00

ROYALAC 150" 0 00 0 00 0 00 0 00 0 25 0 25 025

SULFUR 21- 10" 2 00 2 00 2 00 2 00 2 00 2 00 2 00

T01AL 231 02 231 02 231 02 231 02 230 27 230 27 230 27

(9) MB-1 is the batch provided as set forth in Table II

( 10) N /-butyl 2 ben othiazole sulfenamide available from Uniroyal Chemical Company ( 1 1) Tetraalkyl (C,₂-C₁₄) thiuram disulfide available from Uniroyal Chemical Company having an average molecular weight of 916 (12) Sulfur available from C P Hall

Results

The compounded stocks prepared above were then sheeted out and cut for cure. The samples were cured for the times and at the temperatures indicated m Table IV and their physical properties evaluated. The results are summarized in

Table IV below. Note that in Table IV, cure characteristics were determined using a Monsanto rheometer ODR 2000 ( 1 ° ARC, 100 cpm)- MH is the maximum torque and ML is the minimum torque. Scorch safety (t_s2) is the time to 2 units above

minimum torque (ML), cure time (t₅₀) is the time to 50% of delta torque above

minimum and cure time (t₉₀) is the time to 90% of delta torque above minimum.

Tensile Strength, Elongation and Modulus were measured following procedures in

ASTM D-412. Examples 1-3 illustrate a rubber composition within the scope of this invention Comparative Examples A-D represents a rubber composition outside the scope of this invention CURED PHYSICAL PROPERTIES

TABLE IV

Comparative Example or Example B C D

Cured Characteristics obtained at 160°C

ML (Ib-in ) 657 695 6.49 7.23 7.65 729 744

MH (lb-in ) 3415 3610 34.18 36.65 34.00 3238 3466

Scorch safety t₅2 (mm) 307 282 335 2.65 542 597 524

Cure time t,₀ (mm) 4.71 432 5.01 4.15 7.95 911 7.69

Cure time t₉₀ (mm) 1023 852 925 843 11.71 1388 11.41

Cured at 160°C Cure Time @ 160°C(mm) 150 150 150 150 175 200 175

100% Modulus (Mpa) 26 23 21 26 23 22 24

300% Modulus (Mpa) 119 102 93 110 102 88 9.8

Tensile Strength (Mpa) 18.0 179 164 190 184 17.8 19.4

Elongation, % at Break 410.0 4900 4900 4900 490.0 520.0 540.0 Hardness, Shoie A. 560 59.0 570 59.0 59.0 57.0 590

Mooney Scorch (MS at 135°C) 3 Pt. Rise Time (min) 10 10 23 27 22

Mooney Vιscosity(ML,_J., at 100°C) ML,₊, 71 62 61 64 66 63 64

Tangent Delta 60^QC (10Hz)

% Strain 0.7 0106 0.118 0115 0110 0.110 0.126 0.122

1.0 0111 0.134 0136 0128 0121 0.137 0.140

2.0 0.139 0171 0.173 0153 0157 0.174 0.161

5.0 0.168 0.187 0189 0185 0.176 0.189 0.179

70 0168 0.190 0.194 0.187 0.176 0.186 0.182 140 0158 0.185 0.191 0.184 0.173 0.182 0.178 TABLE IV (CONT'E⁾)

Comparative Ex;ample or A B C D I 2 3 Example

Dynamic Modulus (G' ,kPa) % Strain

0.7 3106 4200 4055 4376 3535 3596 3902

1.0 2902 3902 3727 4017 3295 3355 3601

2.0 2495 3090 3038 3358 2683 2670 2880

50 1874 2299 2242 2478 2092 2039 2248

7.0 1722 2066 2010 2222 1927 1869 2020

14.0 1427 1608 1560 1720 1519 1492 1597

It can be seen from the above data that the examples containing a high

molecular weight thuiram disulfide and a polyalkylene oxide (Examples 1-3) provide

equivalent to improved performance when compared to the examples containing

DPG with no polyalkylene oxide present therein (Comparative Example A) and a

polyalkylene oxide with DPG (Comparative Examples B-D). The mooney scorch

values for Examples 1 -3 λvere significantly higher than those of Comparative

Examples A-D.

Additionally, the 100% and 300% Modulus and % elongation for

Examples 1-3 are comparable to those of Examples A-D. Thus, by replacing 1 phr of

diphenyl guanidine with 0.25 phr of tetraalkyl (C_|2-C₁₄) thiuram disulfide, the scorch

safety of the rubber composition has been significantly improved without any

sacrifice in physical properties resulting in an economical cost advantage being

realized. COMPARATIVE EXAMPLES E-H AND EXAMPLES 4-6

Employing the ingredients indicated in Tables V and VI (which are listed in parts per hundred of rubber by weight), several rubber compositions were compounded in the following manner: the ingredients indicated in Table V were added to an internal mixer and mixed until the materials are incorporated and

thoroughly dispersed and discharged from the mixer. Discharge temperatures of

about 160°C are typical. The batch is cooled, and is reintroduced into the mixer

along with the ingredients indicated in Table VI. The second pass is shorter and dischaige temperatures generally run between 93-105°C

TABLE V - PHASE I

Comp Ex /Ex E F G H 4 5 6

SOLFLEX 1216 75 00 75 00 75 00 75 00 75 00 75 00 75 00

BUDENE 1207 25 00 25 00 25 00 25 00 25 00 25 00 25 00

ZEOSIL 1 165 85 00 85 00 85 00 85 00 85 00 85 00 85 00

N234 5 00 5 00 5 00 5 00 5 00 5 00 5 00

SILQUEST A 1289 6 80 0 00 0 00 0 00 0 00 0 00 0 00

DEG/S1LQUEST

A 1289 BLEND¹³ 0 00 6 80 0 00 0 00 6 80 0 00 0 00

DIPROPYLENE

GLYCOL/S1LQUEST

A 1289 BLEND'³ 0 00 0 00 0 00 6 80 0 00 0 00 6 80

TRIETHYLENE

GLYCOL/SJLQUEST

A 1289 BLEND¹³ 0 00 0 00 6 80 0 00 0 00 6 80 0 00

STEAR1C ACID 1 00 1 00 1 00 1 00 1 00 1 00 1 00

FLEXZONE 7P 1 00 1 00 1 00 1 00 1 00 1 00 1 00

SUNPROOF

IMPROVED 0 50 0 50 0 50 0 50 0 50 0 50 0 50

AROMATIC OIL 44 00 44 00 44 00 44 00 44 00 44 00 44 00

NAUGARD '⁴ 1 00 1 00 1 00 1 00 1 00 1 00 1 00

MB2 TOTAL 244 30 244 30 244 30 244 30 244 30 244 30 244 30

(13) Polyalkylene oxide/silquest blends are physical blends added to the mix as a combination (14) TMQ, an antioxidant available from Uniroyal Chemical.

After the ingredients listed in Table V were mixed and subjected to

processing conditions to form the batch as described above, 4.00 phr of zinc oxide

was added to each of the batches to bring the total of the MB-2 batch to 248 30 phr

for each of the examples. The ingredients listed below in Table VI were then added to the MB-2 batches as set forth below. TABLE VI - PHASED II

Comp E /Ex E F G H 4 5 6

MB-2'⁵ 24830 24830 24830 24830 24830 24830 24830

Delac NS'⁶ 1 50 1 50 1 50 1 50 1 50 1 50 1 50 Diphenyl

Guanadine 200 200 200 200 000 000 000

ROYALAC 150 000 000 000 000 025 025 025

SULFUR 180 180 180 180 I 80 180 180

TOTAL ■360 25360 25360 25360 25185 25185 25185 ( 15) MB-2 is the batch provided as set forth in Table V together with 4 00 phr of zinc oxide

(16) N-.-bufyl-2-bezothιazole sulfenamide available fiom Uniroyal Chemical Company

Results The compounded stocks prepared above were then sheeted out and cut

for cure. The samples were cured for the times and at the temperatures indicated in

Table VII and their physical properties evaluated The results are summarized in

Table VII below. Note that in Table VII, cure characteristics were determined using a Monsanto rhcometer ODR 2000 (1 ° ARC, 100 cpm): MH is the maximum torque and ML is the minimum torque. Scorch safety (t_s2) is the time to 2 units above

minimum torque (ML), cure time (t₅₀) is the time to 50% of delta torque above minimum and cure time (t₉₀) is the time to 90% of delta torque above minimum.

Tensile Strength, Elongation and Modulus were measured following procedures in

ASTM D-412. Examples 4-6 illustrate a rubber composition within the scope of this

invention Comparative Examples E-H represents a rubber composition outside the

scope of this invention. CURED PHYSICAL PROPERTIES

TABLE VII

Comparative Example or Example G H

Cuied Characteristics obtained at 160°C

ML (lb-in ) 39 50 46 48 63 92 55

MH (lb-in ) 284 357 348 367 372 357 380

Scorch safety t₅2 (mm) 36 05 09 03 16 29 03

Cure time t₅₀ (mm) 56 37 45 46 58 51 71

Cure time t,₀ (mm) 220 145 162 137 168 119 177

Stress/Strain Unagedat 160°C Cure Time @ 160°C (mm) 250 170 195 170 195 150 205

100%, Modulus (Mpa) 32 27 27 22 23 21 22

300% Modulus (Mpa) 144 112 110 85 97 85 93

I ensile Strength (Mpa) 183 179 185 192 192 188 184

Elongation, % at Bieak 3500 4300 4400 5600 5000 5200 4900 Hardness, Shore A 670 700 680 670 670 660 670

Mooney Scorch (MS at 135°C) 3 Pt Rise Time (mm) 150 94 119 136 169 146 235

18 Pt Rise Time (mm) 221 133 169 179 205 170 293

ML 84 83 86 83 80 87 81

Stress Relaxation (%) 706 716 672 761 844 735 811

Tangent Delta 60°C ( 10Hz) ΓRPA-2000]

% Strain 07 0088 0061 0063 0051 0052 0037 0053 10 0096 0060 0075 0062 0058 0040 0058 20 0119 0086 0084 0084 0076 0061 0081 50 0156 0141 0134 0136 0132 0125 0130

70 0156 0151 0142 0147 0145 0135 0138 140 0172 0189 0176 0189 0185 0174 0176 TABLE VII (CONT'D)

Comparative Example or

Example E F G H 4 5 6 Dynamic Modulus (G', Kpa)

% Strain

0.7 4800 6687 6694 7620 8002 7161 6832

1.0 4497 6443 6399 7186 7782 6967 6547

2.0 3866 5768 5746 6451 6959 6476 5902 5.0 3020 4303 4069 4681 4945 4635 4281

7.0 2750 3736 3522 4001 4246 3989 3792

14.0 2068 2309 2390 2517 2733 2639 2455 Din Abrasion

Volume Loss (mm³) 84.3 93.5 92 4 103.2 99.9 102.7 92.0 Abrasion Index 147.2 132.8 134.2 120 1 124 2 120.8 134.8

It can be seen from the above data that the examples containing a high molecular weight thiuram disulfide and a polyalkylene oxide (Examples 4-6) provide superior performance when compared to the examples containing DPG with no polyalkylene oxide present therein (Comparative Example F) and a polyalkylene oxide with DPG (Comparative Examples F-H).

When comparing Example 4 and Comparative Example F, the mooney scorch value was significantly higher without any sacrifice in other physical

properties, e.g., tangent delta value, by replacing DPG with a high molecular weight

thiuram disulfide. Additionally, the cure time for Example 4 was relatively equivalent to that of Comparative Example F.

Examples 5 and 6 likewise possessed a significantly higher mooney scorch value when compared to Comparative Examples G and H, respectively, while

also having relatively equivalent cure times. The tangent delta value for Examples 5 and 6 was lower than that of Comparative Examples G and H, which is desirable in

rubber compositions.

Additionally, the 100% and 300% Modulus and % elongation for

Examples 4-6 were either comparable or better than those of Examples E-H. Thus,

by replacing 2 phr of diphenyl guanadine with 0.25 phr of tetralkyl (C₁₂-C₎₄) thiuram

disulfide, the scorch safety of the rubber composition has been significantly

improved without any sacrifice in physical properties resulting in an economical cost

advantage being realized.

Although the invention has been described in its preferred form with a

certain degree of particularity, obviously many changes and variations are possible

therein and will be apparent to those skilled in the art after reading the foregoing

description. It is therefore to be understood that the present invention may be

presented otherwise than as specifically described herein without departing from the

spirit and scope thereof.

Claims (1)

1. WHAT IS CLAIMED IS:

   1. A rubber composition comprising (a) a rubber component; (b) a silica filler; (c) a coupling agent; (d) a cure-enhancing amount of a polyalkylene oxide; and (e) a thiuram disulfide having a molecular weight of at least about 400.

   2. The rubber composition of Claim 1 wherein the rubber component is selected from the group consisting of natural rubber, homopolymers of conjugated diolefins, copolymers of conjugated diolefins and ethylenically unsaturated monomers and mixtures thereof.

   3. The rubber composition of Claim 1 wherein the rubber component is selected from the group consisting of natural rubber, cis-polyisoprene, polybutadiene, poly(styrene-butadiene), styrene-isoprene copolymers, isoprene- butadiene copolymers, styrene-isoprene-butadiene tripolymers, polychloroprene, chloro-isobutene-isoprene, nitrile-chloroprene, styrene-chloroprene, poly (acrylonitrile-butadiene) and ethylene-propylene-diene terpolymer.

   4. The rubber composition of Claim 1 wherein the silica filler is selected from the group consisting of silica, precipitated silica, amorphous silica, vitreous silica, fumed silica, fused silica, synthetic silicate, alkaline earth metal silicate, highly dispersed silicate and mixtures thereof.

   5. The rubber composition of Claim 1 wherein the coupling agent is a sulfur-containing coupling agent.

   6. The rubber composition of Claim 5 wherein the sulfur-containing coupling agent is of the general formula:

   Z-R' -S_n-R²-Z in which Z is selected from the group consisting of

   R³ R³ R⁴

   — Si— R³, — Si— R⁴ — Si— R⁴

   R⁴ R⁴ R⁴ wherein R³ is an alkyl group of from 1 to 4 carbon atoms, cyclohexyl or phenyl; and R⁴ is an alkoxy of from 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms; and R¹ and R² are independently a divalent hydrocarbon of from 1 to 18 carbon atoms and n is an integer of from about 2 to about 8.

   8. The rubber composition of Claim 1 wherein the polyalkylene oxide is selected from the group consisting of dimethylene glycol, diethylene glycol, dipropylene glycol, trimethylene glycol, triethylene glycol, tripropylene glycol, polyethylene oxide, polypropylene oxide, polybutylene oxide and mixtures thereof.

   9. The rubber composition of Claim 1 wherein the thiuram disulfide is of the general formula

   wherein R¹, R², R³ and R⁴ each are the same or different and are hydrocarbons containing from about 4 to about 30 carbon atoms, optionally containing one or more heterocyclic groups, or R' and R² and/or R³ and R⁴ together with the nitrogen atom to which they are bonded are joined together to form a heterocyclic group, optionally containing one or more additional heterocyclic atoms.

   10. The rubber composition of Claim 9 wherein R', R², R³ and R⁴ each are the same or different and are hydrocarbons containing from about 8 to about 18 carbon atoms.

   1 1. The rubber composition of Claim 9 wherein R', R², R³ and R⁴ each are hydrocarbons of between 12 and 14 carbon atoms.

   12. The rubber compositions of Claim 9 wherein the polyalkylene oxide is diethylene glycol and R¹, R², R³ and R⁴ each are hydrocarbons of between 12 and 14 carbon atoms.

   13. The rubber composition of Claim 1 wherein the silica filler is present in an amount of from about 5 to about 100 phr, the coupling agent is present in an amount of from about 0.5 to about 10 phr, the polyalkylene oxide is present in an amount of from about 0.5 to about 10 phr and the thiuram disulfide is present in an amount of from about 0.1 to about 1.0 phr.

   14. The rubber composition of Claim 12 wherein the silica filler is present in an amount of from about 5 to about 100 phr, the sulfur-containing coupling agent is present in an amount from about 0.5 to about 10 phr, diethylene glycol is present in an amount of from about 0.5 to about 10 phr and the thiuram disulfide is present in an amount from about 0.1 to about 1.0.

   15. A method for increasing the mooney scorch value of a rubber composition which comprises the step of forming a rubber composition comprising (a) a rubber component; (b) a silica filler; (c) a coupling agent; (d) a polyalkylene oxide; and (e) a thiuram disulfide having a molecular weight of at least about 400.

   16. The method of Claim 15 wherein the coupling agent is a sulfur- containing coupling agent of the general formula:

   Z-R' -S -R²-Z in which Z is selected from the group consisting of

   R³ R³ R⁴

   — Si— R\ — Si— R⁴ — Si— R⁴

   _R4 _R4 _R4 wherein R³ is an alkyl group of from 1 to 4 carbon atoms, cyclohexyl or phenyl; and R⁴ is an alkoxy of from 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms; and R' and R² are independently a divalent hydrocarbon of from 1 to 18 carbon atoms and n is an integer of from about 2 to about 8.

   17. The method of Claim 15 wherein the thiuram disulfide is of the general formula

   wherein R', R², R³ and R⁴ each are the same or different and are hydrocarbons containing from about 4 to about 30 carbon atoms, optionally containing one or more heterocyclic groups, or R¹ and R² and/or R³ and R⁴ together with the nitrogen atom to which they are bonded are joined together to form a heterocyclic group, optionally containing one or more additional heterocyclic atoms.

   18. The method of Claim 17 wherein R¹. R², R³ and R⁴ each are the same or different and are hydrocarbons containing from about 8 to about 18 carbon atoms.