Patent Application
20080027162
For a further understanding of the invention, drawings are provided as FIGURES (
For the drawings,
Box A of the FIGURES represents the area bounded by the most preferred and limitive combination of 1 through 3 phr for the zinc oxide and 3 through 5 phr for the stearic acid.
Box B of the FIGURES represents a somewhat enlarged the area (as compared to Box A) bounded by a somewhat enlarged combination of 1 through 3 phr for the zinc oxide and 3 through 8 phr for the stearic acid.
Box C of the FIGURES represents an enlarged area bounded by the broader combination of 1 through 7 phr for the zinc oxide and 3 through 8 phr for the stearic acid.
In one limitive aspect of the invention not illustrated by but contained within the aforesaid boundaries of Box A, Box B and Box C of the FIGURES, the weight ratio of stearic acid to zinc oxide is preferably at least 1/1 (e.g. a weight ratio of 1/1 or greater).
Sulfur vulcanizable rubber mixtures containing silica reinforcement were prepared in a manner similar to Example I utilizing a silica coupler and a combination of zinc oxide and stearic acid based long chain (fatty) carboxylic acid.
The silica coupler was an alkoxyorganomercaptosilane having its mercapto moiety blocked (Silica coupling agent A) for Sample H, or bis(3-triethoxysilylpropyl) polysulfide (Silica coupling agent B) for Samples I and J.
The ingredients are illustrated in the following Table 3 and expressed in terms of weight (parts or phr) or weight percent unless otherwise indicated.
1Solution polymerization prepared styrene/butadiene rubber as Solflex 28X42 ™ from The Goodyear Tire & Rubber Company
2Obtained as BUD1254 ™ from The Goodyear Tire & Rubber Company as an oil extended cis 1,4-polybutadiene rubber composed of 100 parts rubber and 25 parts rubber processing oil (40 parts rubber plus 10 parts oil)
3ASTM N-330, an ASTM designation for a rubber reinforcing carbon black
4Precipitated silica as said 1165 ™ from Rhodia
5Coupling agent as NXT ™ from GE Silicones, as an alkoxyorganomercaptosilane having its mercapto moiety blocked
6Coupling agent as said Si266 ™ from Degussa.
7Stearic acid comprised primarily of stearic acid (at least 90 weight percent stearic acid and a minor amount of other organic carboxylic acids comprised of palmitic and oleic acids) and referred to herein as “stearic acid”
8Of the p-phenylenediamine type
9Sulfenamide and guanidine based sulfur cure accelerators
The following Table 4 illustrates cure behavior and various physical properties of the rubber Samples obtained in the manner of Example I.
The footnoted (superscripted) physical test procedures in Table 4 are those reported for the aforesaid Table 2 of Example I.
From Table 4 it can be seen that the use of 3 phr of zinc oxide and 2 phr of stearic acid when used in the silica-rich rubber composition with the alkoxyorganomercaptosilane coupling agent (Coupling agent “A”) in rubber Sample H provided a low uncured viscosity (Mooney viscosity value of 58) and low uncured modulus G′ (G′ value of 146 kPa).
However, the use of the same levels of zinc oxide (3 phr) and stearic acid (2 phr) in a silica-rich rubber composition with the bis(3-triethoxysilylpropyl) disulfide coupling agent (Coupling agent “B”) in rubber Sample I provided a significantly higher uncured viscosity (Mooney viscosity value of 71) and uncured modulus G′ (G′ value of 241 kPa).
In contrast, for rubber Sample J, the use of the coupling agent B, bis(3-triethoxysilylpropyl) polysulfide, with an increased level of the zinc oxide (level of 6 phr) and stearic acid (4 phr), the uncured viscosity (Mooney viscosity value of 51) was significantly reduced as well as the modulus G′ (modulus G′ value of 128 kPa).
This behavior was also observed in Example I with an increasing level of stearic acid and the results from Example I would suggest that the zinc oxide level could be reduced to much lower levels (e.g. to levels of 3 phr or less) for a cost savings without losing the aforesaid uncured rubber viscosity (Mooney viscosity) benefit.
It is also apparent from Table 4 that the low uncured rubber viscosity (Mooney viscosity) is obtained in rubber Sample J without a sacrifice of other indicated cured rubber physical properties.
Accordingly, such results show the ability to achieve substantially equal performance (physical properties) in the silica-rich, diene-based rubber compositions with a lower cost coupling agent, namely the bis(3-triethoxysilylpropyl) polysulfide coupling agent, in place of the significantly more costly and somewhat different chemistry oriented alkoxyorganomercaptosilane coupling agent while achieving the uncured rubber viscosity benefit by the inclusion of the controlled amounts of a combination of zinc oxide and stearic acid in which both of the zinc oxide and stearic acid are blended with the rubber composition in the same mixing step.
Sulfur vulcanizable rubber mixtures containing silica reinforcement were prepared in a manner similar to Example I which contained a combination of zinc oxide and stearic acid, (Samples K and L), and a combination of zinc oxide, stearic acid and zinc soap (Sample M).
The ingredients are illustrated in the following Table 5 and expressed in terms of weight (phr) or weight percent unless otherwise indicated.
1Obtained as Solflex 28X42 ™ from The Goodyear Tire & Rubber Company
2Obtained as BUD1254 ™ from The Goodyear Tire & Rubber Company in a form of 40 parts rubber plus 10 parts rubber processing oil
3ASTM N-330, an ASTM designation for a rubber reinforcing carbon black
4Precipitated silica as said 1165MP ™ from Rhodia
5Coupling agent as said Si266 ™ from Degussa
6Coupling agent as said NXT ™ from GE Silicones
7Fatty acid as stearic acid and a minor amount of other acids including palmitic and oleic acids
8Of the p-phenylenediamine type
9Sulfenamide and guanidine based sulfur cure accelerators
10Zinc soap as EF 44A ™ from the Struktol company, a proprietary zinc soap
The following Table 6 illustrates cure behavior and various physical properties of the rubber Samples expressed in terms of weight (phr) and weight percent except where otherwise indicated. Where a cured rubber sample was evaluated, such as for the stress-strain, rebound, hardness, tear strength and abrasion measurements, the rubber sample was cured for about 14 minutes at a temperature of about 160° C.
The footnoted (superscripted) physical test procedures in Table 4 are those reported for the aforesaid Table 2 of Example I.
From Table 6 it can be seen that the processability of the silica-containing rubber compositions can be improved by use of the indicated combination of zinc oxide and stearic acid for the bis(3-ethoxysilylpropyl) polysulfide silica coupling agent having an average in a range of from about 2 to about 2.6 sulfur atoms in its polysulfidic bridge together with a conventional zinc soap processing aid.
This is considered herein to be significant in the sense of the uncured G′ and uncured Mooney viscosity properties of the rubber composition.
However, from Table 6 it can also be seen than the DIN abrasion value of the cured Sample M was very high, namely 169, as compared to Samples K and L. This is considered herein as meaning that the processability of the uncured rubber composition was obtained with the addition of the zinc soap at the expense of resistance to wear (the increased DIN abrasion value) of Sample M.
Sample M in which a combination of the zinc oxide, stearic acid and zinc soap is used shows a significantly lower tensile strength at break which is considered herein to be a negative impact upon the rubber Sample properties.
While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.
