Masterbatch preparation of silica rich rubber composition, rubber composition and tire with component

Abstract

The invention relates to masterbatch preparation of a silica rich rubber composition, rubber compositions thereof and tire with component.

Claims

1. A method for preparation of a rubber composition comprised of at least two diene-based elastomers with precipitated silicas comprised of (1) a precipitated silica pre-treated with a silica coupling agent and (2) a precipitated silica together with a silica coupling agent, wherein said method is comprised of, based on parts by weight per 100 parts by weight rubber (phr): (A) preparation of a first masterbatch comprised of: (1) at least two conjugated diene-based elastomers, and (2) about 40 to about 200 phr of reinforcing filler comprised of rubber reinforcing carbon black and precipitated silica together with silica coupling agent for said precipitated silica having a moiety reactive with hydroxyl groups on said precipitated silica and another different moiety interactive with said conjugated diene-based elastomers, (B) preparation of a second masterbatch comprised of: (1) at least two conjugated diene-based elastomers, and (2) about 40 to about 200 phr of reinforcing filler comprised of rubber reinforcing carbon black and precipitated silica pre-treated with a silica coupling agent having a moiety reactive with hydroxyl groups on said precipitated silica and another different moiety interactive with said conjugated diene-based elastomers, (treated prior to its addition to the rubber composition), (C) blending said first and second masterbatches together to form a blended rubber composition, (1) together with sulfur curatives comprised of sulfur and at least one sulfur vulcanization accelerator, or (2) thereafter blending sulfur curatives with said blended rubber composition where the sulfur curatives are comprised of sulfur and at least one sulfur vulcanization accelerator.

2. The method of claim 1 wherein said conjugated diene-based elastomers are comprised of styrene/butadiene rubber and cis 1,4-polybutadiene rubber.

3. The method of claim 1 wherein said silica coupling agents for said precipitated silica and said pre-treated precipitated silica are comprised of at least one of alkoxyorganomercaptosilane and bis(3-triethoxysilypropyl) polysulfide containing an average of from 2 to about 4 connecting sulfur atoms in its polysulfidic bridge.

4. The method of claim 1 wherein said silica coupling agent for said precipitated silica of said first masterbatch is comprised of said bis(3-triethoxysilylpropyl) polysulfide.

5. The method of claim 1 wherein said silica coupling agent for said pre-treated precipitated silica of said second masterbatch is an alkoxyorganomercaptosilane.

6. The method of claim 1 wherein weight ratio of said precipitated silica of said first masterbatch and said pre-treated precipitated silica of said second masterbatch is in a range of from about 4/1 to about 1/4.

7. The method of claim 2 wherein the weight ratio of said styrene/butadiene rubber to said cis 1,4-polybutadiene rubber in said first masterbatch is in a range of from about 10/1 to about 1/10 and in said second masterbatch is in a range of from about 10/1to about 1/10, wherein the weight ratio of said styrene/butadiene rubber to said cis 1,4-polybutadiene rubber in said masterbatch blend is in a range of from about 10/1 to about 5/1.

8. The method of claim 1 wherein at least one of said first and second masterbatches further contains from about 5 to about 20 phr of at least one additional conjugated diene based elastomer comprised of at least one of polymers of at least one of isoprene and 1,3-butadiene and styrene with at least one of isoprene and 1,3-butadiene.

9. The method of claim 1 wherein at least one of said first and second masterbatches further contains from about 5 to about 20 phr of at least one additional conjugated diene based elastomer comprised of cis 1,4-polyisoprene rubber.

10. The method of claim 1 wherein each of said first and second masterbatches is individually mixed to a temperature in a range of from about 140? C. to about 170? C.

11. The method of claim 1 wherein said first and second masterbatches are mixed together with sulfur curative comprised of sulfur and at least one sulfur vulcanization accelerator.

12. The method of claim 2 wherein said first and second masterbatches are mixed together with said sulfur and vulcanization accelerators to a temperature in a range of from about 100? C. to about 130? C.

13. The method of claim 1 wherein said first and second masterbatches are mixed together to form a blended rubber composition following which sulfur and vulcanization accelerators are subsequently added to the blended rubber composition in a separate mixing step.

14. The method of claim 1 wherein said first and second masterbatches are mixed together to form a blended rubber composition to which additional precipitated silica is blended with said blended masterbatches following which said sulfur and sulfur vulcanization accelerator(s) are subsequently blended therewith in a separate mixing step.

15. The method of claim 14 wherein said added precipitated silica is reacted with residual silica coupling agent contained in the rubber composition without addition of coupling agent to the blended masterbatches.

16. A rubber composition comprised of a blend of said masterbatches of claim 1 wherein: (A) a first composite of rubber composition of said first masterbatch comprised of said at least two conjugated diene-based rubbers coupled to said precipitated silica with said silica coupler, where said silica coupler has a moiety reactive with hydroxyl groups on said precipitated silica and another different moiety interactive with said diene-based elastomer(s), and (B) a second composite of rubber composition of said second masterbatch comprised of said at least two conjugated diene-based rubbers coupled to said pre-hydrophobated precipitated silica comprised of precipitated silica pre-treated with silica coupler (coupling agent), where said silica coupler has a moiety reactive with hydroxyl groups on said precipitated silica and another different moiety interactive with said diene-based elastomer(s), wherein said rubber composition is comprised of said pre-treated (pre-hydrophobated) precipitated silica and said precipitated silica in a weight ratio thereof in a range of from about 4/1 to about 1/4.

17. A rubber composition comprised of the rubber composition of claim 16 as a blend thereof with sulfur curatives comprised of sulfur and at least one sulfur vulcanization accelerator.

18. A rubber composition is comprised of the rubber composition of claim 16 as a blend thereof with an additional precipitated silica.

19. A rubber composition prepared by the method of claim 1.

20. A tire having a component comprised of the rubber composition of claim 19.

21. A tire having a component comprised of the rubber composition of claim 16.

22. A tire having a tread comprised of the rubber composition of claim 16.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 (FIG. 1) is provided to show preparation of a rubber composition by a process of dual masterbatch preparation of separate rubber compositions and blending of the masterbatches to form a blended rubber composition (non-productive mixing) followed by a separate and final mixing step for addition of sulfur curatives to the blended rubber composition (productive mixing).

THE DRAWINGS

(2) In FIG. 1, Master Batch No. 1 relates to non-productive mixing of diene-based elastomer(s) with reinforcing filler which is based upon precipitated silica and silica coupling agent for the precipitated silica. The diene-based elastomers are not specifically referred to in the drawing.

(3) In FIG. 1, master batch No. 2 relates to non-productive mixing of diene-based elastomer(s) with reinforcing filler which is based upon pre-hydrophobated precipitated silica. The pre-hydrophobated precipitated silica is a precipitated silica pre-reacted with a silica coupling agent. The diene-based elastomers are not specifically referred to in the drawing.

(4) In this manner, in master batch No. 1 the precipitated silica and silica coupling agent are allowed to react in situ within the rubber composition with each other and with diene-based elastomers of the rubber composition to from a precipitated silica reinforced rubber network.

(5) In this manner in master batch No. 2, the pre-hydrophobated precipitated silica is allowed to react in situ within the rubber composition with diene-based elastomers of the rubber composition to from a precipitated silica reinforced rubber network.

(6) It is a significant feature of process that the initial reaction of the silica coupling agent in master batch No. 1 with the precipitated silica and diene-based elastomers is kept separate from the reaction of the pre-hydrophobated silica with the diene-based elastomers in master batch No. 2.

(7) In FIG. 1, it is further shown that an additional, optional, non-productive mixing of the masterbatch blend is provided.

(8) In FIG. 1, it is further shown that an optional addition of precipitated silica (without an accompanying silica coupling agent) to the masterbatch blend is provided.

(9) In FIG. 1, a separate and final mixing step is shown in which sulfur curatives are added to the rubber composition comprised of the masterbatch blend.

(10) The following examples are provided to further illustrate the invention. The parts and percentages are by weight unless otherwise indicated.

EXAMPLE I

(11) Control A and Control B rubber Samples were prepared as separate individual masterbatches of rubber compositions. The masterbatches of Control rubber Sample A and Control rubber Sample B were not blended together. Thereafter, in a subsequent and separate mixing step sulfur curatives (sulfur and accelerators) were blended with each of the masterbatches.

(12) The masterbatch of Control rubber Sample A contained precipitated silica, together with silica coupler and a minor amount of rubber reinforcing carbon black as filler reinforcement for the rubber composition.

(13) The masterbatch of Control rubber Sample B contained pre-hydrophobated precipitated silica (precipitated silica pre-treated with silica coupler) and a minor amount of rubber reinforcing carbon black as filler reinforcement for the rubber composition.

(14) The masterbatch of Control rubber Sample A was a silica-rich rubber sample comprised of a blend of elastomers (styrene/butadiene and cis 1,4-polybutadiene elastomers) together with reinforcing fillers comprised of a minor amount of rubber reinforcing carbon black and a major amount of precipitated silica, together with coupling agent for the precipitated silica. The precipitated silica was coupled in situ (coupled within the rubber composition) to the diene-based elastomer by the coupling agent. In a subsequent and separate mixing step, sulfur curatives (sulfur and accelerator) where added following which the rubber composition was sulfur cured at an elevated temperature and pressure.

(15) The masterbatch of Control rubber Sample B, was a silica-rich rubber sample similar to Control rubber Sample A except that, and contrary to Control rubber sample A, the precipitated silica was a pre-treated (pre-hydrophobated) precipitated silica comprised of precipitated silica pre-treated (pre-hydrophobated) with a silica coupling agent to form a composite thereof and the composite added to the rubber composition. In a subsequent and separate mixing step, sulfur curatives (sulfur and accelerator) were added following which the rubber composition was sulfur cured at an elevated temperature and pressure.

(16) The general formula for masterbatches for Control rubber Samples A and B, together with subsequently added sulfur curatives, are illustrated in the following Table 1.

(17) TABLE-US-00001 TABLE 1 Materials Parts by Weight Non-productive Mixing Step(s) Styrene/butadiene rubber.sup.1 85 Cis 1,4-polybutadiene rubber.sup.2 15 Rubber reinforcing carbon black.sup.3 5 Rubber processing oil 21 Fatty acids.sup.4 5 Wax 1.5 Zinc oxide 1 Resin.sup.5 7.5 Antioxidants 3 Processing aid 2 Precipitated silica.sup.6 85 and 0 Silica coupler.sup.7 7 and 0 Pre-hydrophobated silica.sup.8 0 and 85 Productive Mixing Step Sulfur 1.6 Sulfur cure accelerators(s).sup.9 4.5 .sup.1Styrene/butadiene rubber as Sprintan 4602? from Trinseo as a styrene/butadiene rubber having a Tg of about ?26? C. and containing end functional groups (for example comprised of siloxy and thiol groups) reactive with hydroxyl groups on precipitated silica .sup.2Cis 1,4-polybutadiene rubber having a Tg (glass transition temperature) of about ?102? C. as BUD 4001? from The Goodyear Tire & Rubber Company .sup.3Rubber reinforcing carbon black as N550, an ASTM designation .sup.4Fatty acids comprised of stearic, oleic and palmitic acids .sup.5Styrene/alphamethylstyrene resin having a softening point of about 85? C., ASTM D28, as Resin 2336? from Eastman Chemical .sup.6Precipitated silica as Zeosil 1156MP? from Solvay .sup.7Silica coupler as Si266? from Evonik comprised of a bis(3-triethoxysilylpropyl) polysulfide having an average of from about 2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge. .sup.8Pre-hydrophobated precipitated silica as precipitated silica pre-treated with an alkoxyorganomercaptosilane as Agilon? 400 from PPG Industries .sup.9sulfur cure accelerators comprised of a combination of sulfenamide and diphenylguanidine.

(18) Various cured and uncured rubber properties for Control rubber Sample A and Control rubber Sample B are reported in the following Table 2.

(19) TABLE-US-00002 TABLE 2 Samples Control A Control B Precipitated silica 85 0 Pre-hydrophobated precipitated silica 0 85 Properties Wet Traction Prediction, Rebound at 0? C. Rebound (%), lower is better 7.2 6.6 Handling Prediction -- Stiffness (Modulus, Storage Modulus G, 11 Hertz, 100? C.) G, 1% strain (MPa), higher is better 2.3 1 G, 10% strain (MPa), higher is better 1.6 0.9 Hysteresis prediction (higher rebound is better for lower hysteresis, better (reduced) tire predictive rolling resistance) Rebound, 60? C., (%), higher is better 54 62 Rebound, 100? C., (%), higher is better 66 73 Tear resistance.sup.1 (Newtons), higher is better 76 60 Grosch Abrasion Rate.sup.2, mg/km abraded away 146 123 (lower is better) medium severity abrasion test .sup.1Data obtained according to a tear strength (tear resistance) test to determine interfacial adhesion between two samples of a rubber composition. Such interfacial adhesion is determined by pulling one rubber composition away from the other at a right angle to the untorn test specimen with the two ends of the rubber compositions being pulled apart at a 180? angle to each other using an Instron instrument at 95? C. and reported as Newtons force. .sup.2The Grosch abrasion rate run on an LAT-100 Abrader and is measured in terms of mg/km of rubber abraded away. The test rubber sample is placed at a slip angle under constant load (Newtons) as it traverses a given distance on a rotating abrasive disk (disk from HB Schleifmittel GmbH). In practice, a low abrasion severity test may be run, for example, at a load of 20 Newtons, 2? slip angle, disk speed of 40 km/hr for a distance of 7,500 meters; a medium abrasion severity test may be run, for example, at a load of 40 Newtons, 6? slip angle, disk speed of 20 km/hr and distance of 1,000 meters.

(20) From Table 2 it is seen that for Control rubber Sample B, utilization of the pre-hydrophobated precipitated silica instead of the precipitated silica (and silica coupler) of Control rubber Sample A resulted in a significantly large beneficial increase in rebound property (beneficial reduction in hysteresis) for rubber Sample B.

(21) From Table 2 it is also seen that for Control rubber Sample B utilization of the pre-hydrophobated precipitated silica instead of the precipitated silica (and silica coupler) of Control rubber Sample A resulted in an improved decrease (improvement) in abrasion resistance and predictive improved wet traction for rubber Sample B.

(22) However, from Table 2 it is further seen that utilization of pre-hydrophobated precipitated silica in rubber Sample B resulted in a reduction of storage modulus G (reduction in stiffness and associated predictive tire handling).

(23) It is concluded that it would be desirable to evaluate whether the storage modulus G property (100? C.) for the rubber composition containing the pre-treated precipitated silica as its reinforcing filler can be beneficially increased while substantially maintaining other beneficial physical properties for the rubber composition.

EXAMPLE II

(24) In view of the results obtained in Example I, it is desired to evaluate promotion of a beneficial increase in the storage modulus G of Control rubber Sample B in which the silica filler reinforcement used for its masterbatch was the pre-hydrophobated precipitated silica.

(25) For such evaluation, it is proposed to blend limited amounts of the masterbatch of of rubber Sample A (containing the precipitated silica and silica coupler which has been reacted in situ within the rubber composition) to the masterbatch for rubber Sample B (containing the pre-hydrophobated silica reinforcement). Silica curatives are then added to the mixed rubber compositions in a separate and additional mixing step. In this manner it is envisioned that a complex network of the diene-based elastomer and precipitated silica reinforcement is created in the mixed rubber compositions.

(26) In one respect, it is considered that the rubber compositions of the first and second masterbatches may substantially retain some of their respective physical property characterizations in the rubber masterbatch blends of the blended rubber compositions in a sense that it is expected that the silica coupling agent (of the masterbatch containing the separately added silica coupling agent) may react to preferentially attach the precipitated silica to the elastomers of the first masterbatch and the pre-hydrophobated precipitated silica may react to preferentially attach its precipitated silica to the elastomers of the second masterbatch.

(27) In a further respect, in the blends of the masterbatches, it is envisioned that the remaining silica coupling agent, which may not have fully reacted with the precipitated silica and elastomers in the first masterbatch, may react with hydroxyl groups which may remain on the pre-hydrophobated precipitated silica of the second masterbatch to create a complex reinforcement network within the rubber composition of the blended masterbatches with the resultant rubber properties being unknown without experimentation.

(28) For such evaluation, as indicated, it is desired to evaluate promoting an increase in the storage modulus G of the pre-hydrophobated silica-containing rubber composition while substantially maintaining other beneficial physical properties.

(29) For such evaluation, the following rubber compositions were prepared:

(30) (A) Experimental rubber Sample C was prepared with a single masterbatch comprised of the elastomers with a 1/1 ratio of the precipitated silica to the pre-hydrophobated precipitated silica. A silica coupler was used for the precipitated silica. In this manner, the silica reinforcement was comprised of a complex network of the silica coupling agent reacting with the precipitated silica and elastomer as well as any remaining hydroxyl groups of the pre-hydrophobated precipitated silica and of the pre-hydrophobated silica with the elastomer.

(31) (B) The fundamental evaluation of this invention was represented as Experimental rubber Sample D. Instead of forming a rubber blend in the manner of rubber Sample C containing both of the precipitated silica and pre-hydrophobated precipitated silica, a blend of separately prepared first and second masterbatches was created based on the formulation presented in Table 1 of Example I. The first masterbatch was provided with precipitated silica (together with its silica coupler) as a reinforcing filler. The second masterbatch was provided with pre-hydrophobated precipitated silica as a reinforcing filler. The ratio of pre-hydrophobated precipitated silica to precipitated silica was 1/1 for masterbatch blend. The pre-hydrophobated precipitated silica and precipitated silica (with its silica coupler) were allowed to react separately with their respective rubber compositions before the masterbatches were mixed together.

(32) By such methodology, the preparation of Experimental rubber Sample C by blending the elastomers with a combination of the precipitated silica (with its silica coupler) and pre-hydrophobated precipitated silica is avoided.

(33) It is believed that such methodology involves evaluation of a novel procedure and resulting product.

(34) (C) Experimental rubber Sample E was prepared in the manner of Experimental rubber Sample D except that additional precipitated silica was added to the to the blend of masterbatches (after the masterbatches are mixed together) and prior to the addition of sulfur curatives.

(35) Various cured rubber properties of the rubber compositions prepared according to separate rubber composition preparations for rubber Control rubber Samples A and B and Experimental rubber Samples C, D and E are reported in the following Table 3.

(36) TABLE-US-00003 TABLE 3 Samples Control Experimental A B C D E Precipitated silica 85 0 43 43 43 Pre-hydrophobated precipitated silica (CTS) 0 85 43 43 43 Properties Wet traction prediction, rebound at 0? C., (%) 7.2 6.6 7.1 6.4 6.6 Handling Prediction -- Stiffness (Modulus, Storage Modulus G, 11 Hertz, 100? C.), G, 1% strain (MPa) 2.3 1.0 1.5 1.7 1.8 G, 10% strain (MPa) 1.6 0.9 1.4 1.4 1.4 Hysteresis Prediction Rebound, 100? C., (%)(higher rebound is better, 66 73 72 73 73 lower tan delta is better) Tear resistance.sup.1 (Newtons) 76 60 60 54 58 Grosch abrasion rate.sup.2, mg/km abraded away 146 123 137 122 125 medium severity abrasion test, (lower is better)

(37) For Table 3 the results for individual Control rubber Samples A and B are reported for Control rubber Samples A and B of Example I. Control rubber Sample B contained the pre-hydrophobated precipitated silica filler reinforcement. It is seen that Control rubber Sample B resulted in a significant beneficial increase in rebound property and an improvement in rate of abrasion yet with a reduction in stiffness property indicated by a reduction in storage modulus G.

(38) It was desired to evaluate obtaining the aforesaid beneficial increase in rebound property of rubber Sample B while improving the stiffness (G) property by providing rubber Sample C in which a blend of the pre-hydrophobated precipitated silica together with the precipitated silica (together with its silica coupling agent) in a 1/1 ratio was provided.

(39) For Experimental rubber Sample C, it is seen that a beneficial rebound property was obtained and the stiffness property (G) was beneficially improved compared to Control rubber Sample B. However the abrasion rate was increased.

(40) A significant aspect of this invention was the preparation of Experimental rubber Sample D as a variation of preparation of Experimental rubber Sample C. For Experimental rubber Sample D, individual and separate masterbatches were prepared in which a first masterbatch contained the precipitated silica and its silica coupling agent. A second masterbatch was prepared which contained the pre-hydrophobated precipitated silica. The first and second masterbatches were mixed following which, in a separate mixing step, the sulfur curatives were blended to form Experimental rubber Sample D.

(41) It is seen from Table 2 that for Experimental rubber Sample D, as compared to Experimental rubber Sample C, that the beneficial rebound property was obtained by application of the masterbatch blending methodology with an improvement in low strain (one percent strain) stiffness (G) and an improved reduction in rate of abrasion (an improved abrasion resistance).

(42) On this basis it is concluded that such individual masterbatch mixing methodology provided an improved rubber composition which is considered as being a significant discovery with the results being unpredictable without this experimentation.

(43) For Experimental rubber Sample E, compared to Experimental rubber Sample D, an addition of precipitated silica was provided to the mixed masterbatches prior to the sulfur curative addition step. It is seen from Table 2 that such precipitated silica addition further improved the low strain stiffness (storage modulus G) of the rubber composition while maintaining the beneficial rebound property and abrasion resistance.

(44) On this basis it is concluded that such mixing methodology and resulting rubber composition presented improvements in the nature of discoveries in both methodology and resulting product, with the results being unpredictable without this experimentation.