RUBBER COMPOSITION COMPRISING A BLOCK-COPOLYMER

Abstract

The present invention is directed to a rubber composition comprising an elastomer, a filler, and a block-copolymer. According to the invention, the block-copolymer comprises (i) an elastomer block and (ii) a thermoplastic block comprising a poly alkylacrylate, wherein the alkylacrylate comprises a polycyclic substituent at its single bonded oxygen atom. Moreover, the present invention is directed to a block-copolymer.

Claims

1. A rubber composition comprising: an elastomer; a filler; and a block-copolymer comprising an elastomer block and a thermoplastic block comprising a poly alkylacrylate, wherein the poly alkylacrylate contains a single bonded oxygen atom, and wherein the alkylacrylate comprises a polycyclic substituent at its single bonded oxygen atom.

2. The rubber composition of claim 1 wherein at least one of the elastomer and the elastomer block comprises at least one diene-based elastomer.

3. The rubber composition of claim 2 wherein the diene-based elastomer is selected from one or more of styrene butadiene rubber, polybutadiene, solution polymerized styrene butadiene rubber, emulsion polymerized styrene butadiene rubber, natural rubber, synthetic polyisoprene, and isoprene butadiene rubber.

4. The rubber composition of claim 1 wherein at least one of the elastomer and the elastomer block has a functional group which is capable of coupling to one of silica and carbon black.

5. The rubber composition of claim 4 wherein the elastomer block comprises an elastomer chain having a first chain end and a second chain end, with the first chain end connected to the poly alkylacrylate block, and wherein the functional group is located at said second chain end.

6. The rubber composition of claim 1 wherein the poly alkylacrylate has the following structure: ##STR00005## wherein n represents the number of the alkylacrylate monomers in the poly alkylacrylate, wherein R.sub.1 represents the alkyl; and wherein R.sub.2 represents a polycyclic hydrocarbon material.

7. The rubber composition of claim 6 wherein n is an integer being one or more of larger than 10 and smaller than 2000.

8. The rubber composition of claim 1 wherein the alkyl is one of —CH.sub.3 and —C.sub.2H.sub.5.

9. The rubber composition of claim 1 wherein the alkylacrylate has at its single bonded oxygen atom one of: i) a bicyclic substituent, ii) a tricyclic substituent, iii) a hydrocarbon substituent comprising at least seven carbon atoms, with at least five of the carbon atoms cyclically arranged.

10. The rubber composition of claim 1 wherein the poly alkylacrylate is one of: poly(isobornyl methacrylate) and poly(adamantyl methacrylate).

11. The rubber composition of claim 6 wherein the poly alkylacrylate comprises one or more of the following structures: ##STR00006##

12. The rubber composition of claim 1 wherein the thermoplastic block consists of the poly alkylacrylate and has one or more of: (i) a number average molecular weight Mn of at least 10,000 g/mol and (ii) at least 10 alkylacrylate monomers.

13. The rubber composition of claim 1, wherein the thermoplastic block consists of the poly alkylacrylate and has one or more of: (i) a number average molecular weight Mn of at most 150,000 g/mol and (ii) at most 2000 alkylacrylate monomers.

14. The rubber composition of claim 1, wherein the elastomer block has one or more of: (i) a number average molecular weight Mn of at least 10,000 g/mol and (ii) at least 90 monomers chosen from a list of styrene, butadiene, and isoprene.

15. The rubber composition of claim 1, wherein the elastomer block has one or more of: (i) a number average molecular weight Mn of at most 450,000 g/mol and (ii) at most 6000 monomers chosen from a list of styrene, butadiene, and isoprene.

16. The rubber composition of claim 1, wherein the block-copolymer has a first glass transition temperature within a range of −92° C. to −15° C. and a second glass transition temperature within a range of 150° C. to 250° C.

17. The rubber composition of claim 1, wherein a ratio of (i) a number average molecular weight Mn of the elastomer block and (ii) a number average molecular weight Mn of the thermoplastic block is within a range of 0.1 to 0.95.

18. The rubber composition of claim 1 comprising: 50 phr to 90 phr of the elastomer; 10 phr to 50 phr of the block-copolymer; 20 phr to 200 phr of the filler comprising one or more of: at least one silica and at least one carbon black.

19. An article of manufacture selected from a tire, a power transmission belt, a hose, a track, an air sleeve, and a conveyor belt, wherein the article of manufacture comprises the rubber composition of claim 1.

20. A block-copolymer comprising an elastomer block, and a thermoplastic block comprising a poly alkylacrylate, wherein the poly alkylacrylate contains a single bonded oxygen atom, and wherein the alkylacrylate comprises a polycyclic substituent at its single bonded oxygen atom, and wherein the block-copolymer is a diblock copolymer.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0066] The invention will be described by way of example and with reference to the accompanying drawings in which:

[0067] FIG. 1 illustrates a schematic cross section through an example tire.

DETAILED DESCRIPTION OF THE INVENTION

[0068] FIG. 1 is a schematic cross-section of a tire 1. The tire 1 has a tread 10, an inner liner 13, a belt structure comprising four belt plies 11, a carcass ply 9, two sidewalls 2, and two bead regions 3 comprising bead filler apexes 5 and beads 4. The example tire 1 is suitable, for example, for mounting on a rim of a vehicle, e.g. a truck or a passenger car. As shown in FIG. 1, the belt plies 11 may be covered by an overlay ply 12. The carcass ply 9 includes a pair of axially opposite end portions 6, each of which is associated with a respective one of the beads 4. Each axial end portion 6 of the carcass ply 9 may be turned up and around the respective bead 4 to a position to anchor each axial end portion 6. One or more of the carcass ply 9, belt plies 11, and overlay ply 12 may have a plurality of substantially parallel reinforcing members made of a fabric material such as polyester, rayon, or similar suitable organic polymeric compounds or made of metal wire. The turned-up portions 6 of the carcass ply 9 may engage the axial outer surfaces of two flippers 8 and axial inner surfaces of two chippers 7. As shown in FIG. 1, the example tread 10 may have four circumferential grooves, each groove essentially defining a U-shaped opening in the tread 10.

[0069] While the embodiment of FIG. 1 suggests a plurality of tire components including for instance apexes 5, chippers 7, flippers 8, and overlay 12, such components are all not mandatory for the invention. Also, the turned-up end of the carcass ply 9 is not necessary for the invention or may pass on the opposite side of the bead area 3 and end on the axially inner side of the bead 4 instead of the axially outer side of the bead 4. The tire could also have, for instance, more or less than four grooves. It shall be emphasized that the present invention focuses on a rubber composition comprising a block-copolymer. Thus, the description of FIG. 1 and its components are merely to be understood as an example without limiting the present invention.

[0070] In an embodiment of the invention, a rubber composition, such as in a rubber component of the tire 1 comprises a solution-polymerized styrene butadiene rubber and a block-copolymer having an elastomer block and a poly (isobornyl methacrylate) block. In an alternative embodiment, the rubber composition may comprise one or more of polybutadiene, natural rubber, solution-polymerized styrene butadiene as an elastomer. Instead of a poly (isobornyl methacrylate) block, the block-copolymer can also comprise a poly (adamantyl methacrylate) block or a block comprising both thermoplastic materials, i.e. (isobornyl methacrylate) units and (adamantyl methacrylate) units within the thermoplastic block.

[0071] Such block-copolymers can be prepared by the person skilled in the art by free radical, ionic, coordination, reversible addition-fragmentation chain transfer (RAFT) or atom transfer radical (ATRP) polymerization, for example.

[0072] This invention is illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.

[0073] In a non-limiting example, isobornyl methycrylate (IBOMA) can be polymerized to PIBOMA via RAFT polymerization using 1,1,2-trichleroethane (TCA) as a solvent at a temperature of 60° C., and by addition of 4-Cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl]pentanoic acid (CDTPA) and α,α,′-Azoisobutyronitrile (AIBN), with an SDTPA:AIBN moler ratio of 4:1, wherein IBOMA is present at 1.44 g/ml or 50%, for a time of 24 hours. After having obtained the thermoplastic PIBOMA (block), styrene and butadiene monomers are added under addition of CDTPA and the initiator 2,2′-Azobis(N-butyl-2-methyl propionamide) (VAM-110) as well as 1,1,2-Trichlorethane (1,1,2-TCA) with an example reaction time of 72 hours and a molar TCA to initiator ratio of about 1:1, all at a temperature of 115° C. It is re-emphasized that this example of a synthesis of the PIBOMA-SBR block-copolymer constitutes a non-limiting example using polymerization techniques known to the person skilled in the art.

[0074] In another non-limiting example, block-copolymers can be synthesized via anionic polymerization in which the first, elastomer block is synthesized out of the elastomer forming monomers in a first step and then the thermoplastic monomers are added in a second step so as to form the second, thermoplastic block of the diblock copolymer. For instance, butadiene is distilled under vacuum into a pressure stable glass reactor pre-cooled at −20° C. Further, the reactor is filled with an inert atmosphere up to 0.1 bar overpressure. A solution of tetraacetylethylenediamine (TMEDA) in cyclohexane is provided in a separate flask and degassed. This solution is injected into the reactor containing the butadiene under overpressure of the inert atmosphere (such as Ar) at −20° C. The reactor is then heated to about 55° C. and the solution is stirred at this temperature for about 20 minutes. A solution of n-BuLi in hexane is injected into the reactor at 55° C. resulting in the formation of poly(butadienyl)lithium (PBD-Li+). Once the injection of n-BuLi is complete, the temperature in the reactor is increased to 60° C. Polymerization of butadiene proceeds at 60° C. for about 1 h, whereupon the temperature is reduced to 45° C. The temperature is further decreased to 25° C. and 1,1-diphenylethylene (DPE) is injected in the reactor to end-cap polybutadiene anions. Stirring is continued for 15 minutes at 25° C. wherein the color of the solution changes from pale yellow to orange-red. Afterwards, the solution is cooled down to 0° C. and tetrahydrofuran (THF) is introduced into the reactor, changing the color of the solution to red. Finally, IBOMA is injected into the reactor at 0° C. such that the color of the solution disappears. The polymerization of IBOMA is proceeded for 1.5 hour at 0° C., whereupon the polymerization is quenched by injection of deoxygenated anhydrous methanol. The resulting block-copolymer can be purified by (double) precipitation into the excess of methanol and dried.

[0075] The inventors have synthetized a plurality of different block-copolymers comprising blocks with varying molecular weights, as well as different elastomer monomer units, and include those in rubber compositions such as shown in TABLE 1 below.

[0076] In particular, TABLE 1 shows two control samples of rubber compositions comprising a SSBR, a filler (here carbon black), oil, stearic acid, antioxidants, waxes, zinc oxide, sulfur and curing accelerators. Control Sample 1 comprises no thermoplastic polymer and is mainly reinforced by means of its carbon black filler, whereas Control Sample 2 (which is also not in accordance with the present invention) comprises 10 phr of polyethylene (PE) which is used for additional reinforcement of the rubber composition.

[0077] Each of the Inventive Examples 1 to 7 comprises a different type of a block-copolymer in accordance with an embodiment of the present invention. None of the Inventive Examples comprises PE. Carbon black, oil, stearic acid, antioxidants, waxes, zinc oxide, sulfur and accelerators, are included at the same weight level as in the Control Samples 1 and 2. Moreover, the Inventive Examples comprise the same type of SSBR as the Control Samples but in slightly varying amounts in view of the varying chain lengths of the elastomer blocks of the utilized block-copolymers. The composition of each of the block-copolymers 1 to 7 is indicated in the footnote of TABLE 1 below.

TABLE-US-00001 TABLE 1 Control Inventive Examples C C IE IE IE IE IE IE IE 1 2 1 2 3 4 5 6 7 Material [phr] SSBR .sup.a 100 100 90 92 94 97 71 81 88 Block- 0 0 20 0 0 0 0 0 0 Copolymer 1 .sup.b Block- 0 0 0 18 0 0 0 0 0 Copolymer 2 .sup.c Block- 0 0 0 0 16 0 0 0 0 Copolymer 3 .sup.d Block- 0 0 0 0 0 13 0 0 0 Copolymer 4 .sup.e Block- 0 0 0 0 0 0 39 0 0 Copolymer 5 .sup.f Block- 0 0 0 0 0 0 0 29 0 Copolymer 6 .sup.g Block- 0 0 0 0 0 0 0 0 22 Copolymer 7 .sup.h PE .sup.i 0 10 0 0 0 0 0 0 0 Carbon 50 50 50 50 50 50 50 50 50 Black Oil .sup.j 4 4 4 4 4 4 4 4 4 Stearic 2 2 2 2 2 2 2 2 2 Acid Anti- 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 oxidants .sup.k Waxes 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Zinc Oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Accel- 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 erators .sup.l .sup.a Sprintan ™ SLR 3402-SCHKOPAU, Solution-styrene butadiene rubber, with a glass transition temperature of about −62° C.; .sup.b Block-copolymer comprising a SSBR block with a Mn of 28700 g/mol and a PIBOMA block with a Mn of 26000 g/mol, wherein the PIBOMA block corresponds to 10 phr; SSBR microstructure: 20 weight % styrene, 17 weight % 1,2-butadiene, 63 weight % 1,4 butadiene; polydispersity 1.6; .sup.c Block-copolymer comprising a SSBR block with a Mn of 26600 g/mol and a PIBOMA block with a Mn of 36700 g/mol, wherein the PIBOMA block corresponds to 10 phr; SSBR microstructure: 18.5 weight % styrene, 16.5 weight % 1,2-butadiene, 65 weight % 1,4 butadiene; polydispersity 1.5; .sup.d Block-copolymer comprising a SSBR block with a Mn of 25900 g/mol and a PIBOMA block with a Mn of 46500 g/mol, wherein the PIBOMA block corresponds to 10 phr; SSBR microstructure: 15 weight % styrene, 17 weight % 1,2-butadiene, 68 weight % 1,4 butadiene; poly dispersity 1.5; .sup.e Block-copolymer comprising a SSBR block with a Mn of 11800 g/mol and a PIBOMA block with a Mn of 40200 g/mol, wherein the PIBOMA block corresponds to 10 phr; SSBR microstructure: 15 weight % styrene, 15 weight % 1,2-butadiene, 70 weight % 1,4 butadiene; polydispersity 1.8; .sup.f Block-copolymer comprising a BR block with a Mn of 78400 g/mol and a PIBOMA block with a Mn of 26800 g/mol, wherein the PIBOMA block corresponds to 10 phr; BR micro structure: 47 weight % 1,2-butadiene, 53 weight % 1,4 butadiene; polydispersity 1.25; .sup.g Block-copolymer comprising a BR block with a Mn of 68500 g/mol and a PIBOMA block with a Mn of 36700 g/mol, wherein the PIBOMA block corresponds to 10 phr; BR micro structure: 52 weight % 1,2-butadiene, 48 weight % 1,4 butadiene; poly dispersity 1.16; .sup.h Block-copolymer comprising a BR block with a Mn of 80230 g/mol and a PIBOMA block with a Mn of 66550 g/mol, wherein the PIBOMA block corresponds to 10 phr; BR micro structure: 51 weight % 1,2-butadiene, 49 weight % 1,4 butadiene; poly dispersity 1.33; .sup.i Ultra-high molecular weight polyethylene with a number average molecular weight Mn of 4,700,000 g/mol as determined by Margolies' equation; .sup.j TDAE oil; .sup.k as Phenylene diamine: .sup.l as Sulfenamides and diphenylguanidine

[0078] TABLE 2 shows measured storage modulus (E′) values for the compositions listed also in TABLE 1, wherein the storage modulus can be considered as a stiffness indicator or in other words as an indicator for the reinforcement effect of PE and the different block-copolymers in the above compositions.

[0079] Control Sample 2 which comprises the additional PE reinforcement shows increased stiffness values below about 100° C. At higher temperatures, the reinforcement of PE drops significantly and even below the values of the Control Sample 1 although Control Sample 2 comprises the same amount of carbon black as Control Sample 1. According to a non-binding theory of the inventors, this is mainly caused by the melting point of the PE material (at about 135° C.).

[0080] Turning to the Inventive Examples, all Inventive Examples show a significantly higher stiffness than Control Samples 1 and 2 at the measured temperatures 30° C., 50° C., and 100° C. Even at 150° C., the stiffness is higher for all Inventive Examples compared with the Control Sample 2. While Inventive Examples 1, 2, 3, 4 and 7 show also a higher storage modulus value at 150° C. in comparison with the Control Sample 1, the storage modulus values for Inventive Examples 5 and 6 are at least at a comparable level at the same temperature compared to Control Sample 1. However, in this context it is emphasized that the stiffness and reinforcement at lower temperatures is significantly higher for Inventive Examples 5 and 6 compared to the Control Sample 1.

TABLE-US-00002 TABLE 2 Control Inventive Examples C C IE IE IE IE IE IE IE Temper- 1 2 1 2 3 4 5 6 7 ature Storage Modulus E′ [MPa]*  30° C. 11.7 12.1 19.2 19.1 17.0 14.3 14.2 16.4 21.4  50° C. 10.4 10.9 16.3 16.3 14.7 12.5 12.3 14.1 18.1 100° C. 9.3 9.2 12.3 13.3 12.9 10.5 9.9 11.0 14.3 150° C. 9.3 7.9 10.2 12.6 12.5 9.8 8.7 9.1 12.4 180° C. 9.1 7.7 8.5 11.3 11.6 9.0 7.8 7.8 10.3 *Dynamic Mechanical Thermal Analysis (DMTA) was performed in accordance with the ASTM D7028-07 standard. Measurements were carried out for cured (vulcanized) compounds on bars (length × width × thickness = 20 × 6 × 2 (mm)) with a DMA 242 C model (Netzsch, Germany) operating in tension mode (strain between 0.05 and 0.07%, pretension: 10-2N). Experiments were performed at 1 Hz frequency with a heating rate of 2° C./min from −180° C. to 180° C.

[0081] Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.