Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-03-16
2002-06-18
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S575000
Reexamination Certificate
active
06407153
ABSTRACT:
TECHNICAL FIELD
The present invention relates to elastomeric compositions containing hydrophobicized silica. Elastomeric compositions of the invention are suitable, for example, for the manufacture of tires, tire tread, hose, industrial drive belts, conveyor belts and shoe soles.
BACKGROUND ART
In recent years, there has developed a considerable interest in silica reinforced tires, particularly since the appearance in 1992 of the Groupe Michelin (G-M) patents (EP 05 01 227 A 1; AU-A-111 77 192) indicating that tires made with tread formulations incorporating silica enjoy some important performance advantages over those based on conventional carbon black filler. Improvements are claimed for this “Green Tire” in the areas of (a) lower rolling resistance, (b) better traction on snow and (c) lower noise generation, when compared with conventional tires filled with carbon black.
Rubber for tires is often supplied by a rubber producer to a tire manufacturer in the form of a masterbatch containing an elastomer, which is typically a hydrocarbon rubber, an oil extender and a filler. The traditional filler has been carbon black in the form of fine particles. These particles have hydrophobic surface characteristics and will therefore disperse easily within the hydrophobic elastomer. In contrast, silica has a very hydrophilic surface and considerable difficulty has been encountered in dispersing silica in the hydrophobic rubber elastomer.
In the past, efforts have been made to make masterbatches from elastomer dispersions and aqueous dispersions of silica pigment, such as those referred to and attempted by Burke, in U.S. Pat. No. 3,700,690. Burke attempted to overcome the previously known difficulties of incorporating fine particles of silica uniformly into a masterbatch. At the time of the Burke invention, there was no known elastomer-silica masterbatch offered in the commercial market. Similarly today, to the Applicant's knowledge, there are no commercially available in situ produced elastomer-silica masterbatches in the market, despite the efforts of Burke (i.e., conventional elastomer-silica masterbatches are produced and available in the dry state).
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate or mitigate at least one of the above-mentioned disadvantages of the prior art.
It is another object of the present invention to provide a novel masterbatch composition.
Thus, in one of its aspects, the present invention provides a rubber masterbatch composition comprising a solution SBR (styrene-butadiene rubber) and silica particles.
In one embodiment, the solution SBR may be a low vinyl, low styrene solution SBR. In another embodiment, the solution SSR may comprise a mixture of a solution SBR (i.e., virtually any solution SBR) and solution BR (butadiene rubber).
In another of its aspects, the present invention provides an elastomeric composition which comprises:
(i) a solution SBR/silica-containing masterbatch, which contains preferably from about 40 to about 120 parts by weight of silica per 100 parts by weight of polymer, and
(ii) a solution BR/silica-containing masterbatch, which contains preferably from about 40 to about 120 parts by weight of silica per 100 parts by weight of polymer;
wherein the silica has been hydrophobicized.
The present compositions may be characterized, inter alia, by being useful in the production of vulcanizates have an improvement in one or more of the following properties: traction, abrasion and rolling resistance.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used throughout this specification, the term “solution SBR” is intended to mean a styrene-butadiene rubber produced by a process in which polymerization of the styrene and butadiene monomers is catalyzed in the presence of a solvent (typically a hydrocarbon solvent). The solution SBR typically has a glass transition temperature (Tg) of between 0° C. and −80° C., when measured by differential scanning calorimeter.
As disclosed hereinabove, in one embodiment of the present invention, the solution SBR may be a single elastomer in the form of a low-vinyl, low styrene solution SBR. The term “low vinyl, low styrene solution SBR”, as used throughout this specification, is meant to encompass a solution SBR having a vinyl content of less than about 40% (preferably in the range of from about 5 to about 40%, more preferably in the range of from about 5 to about 30%, most preferably in the range of from about 5 to about 25%) and a styrene content in the range of from about 5 to about 25% (preferably in the range of from about 10 to about 25%, most preferably in the range of from about 15 to about 25%). In this embodiment, the composition comprises a masterbatch of the low vinyl, low styrene solution SBR and the silica particles.
As further disclosed hereinabove, in another embodiment of the present invention, the solution SBR may comprise a mixture of a solution SBR and a solution BR. In a first version of this embodiment, the composition comprises a mixture of a first masterbatch comprising solution SBR/silica particles and a second masterbatch comprising solution BR/silica particles. In a second version of this embodiment, the composition comprises a single masterbatch derived from a mixture of polymer cements—i.e., a mixture of solution SBR and solution BR cements is first made and then contacted with the silica particles to produce the masterbatch.
The solution SBR may be suitably prepared in solution and may have a styrene content in the range of from about 15 to about 25% by weight and a glass transition temperature (Tg) of between 0° C. and −80° C., when measured by differential scanning calorimeter. The content of vinyl bonds in the butadiene fraction incorporated can be in the range of from about 30 to about 75%, preferably in the range of from about 50 to about 75%. The content of trans-1,4 bonds can be between 15 and 60%, and the content of cis 1,4 bonds is complementary to the content of vinyl bonds plus trans-1,4 bonds. The vinyl bonds content of the copolymer is preferably greater than 50%. Particularly preferred is Buna VSL 5025-1 (formerly Buna VSL 1950S25, commercially available from Bayer Inc.) which is a co-polymer of styrene and butadiene, the styrene content being about 25% and the vinyl content in the butadiene portion being about 67%.
As used throughout this specification, the term “solution BR” is intended to mean a butadiene rubber produced by a process in which polymerization of the butadiene monomer is catalyzed in the presence of a solvent (typically a hydrocarbon solvent). Preferably, the solution BR is a high cis polybutadiene, more preferably a solution BR having more than 90% cis-1,4 bonds. The production of such a solution BR can be achieved by known methods of catalysis with the use of transition metals as described, for instance in French Patent No. 143 6607. A particularly preferred solution BR is Taktene 1203 (available from Bayer), which has a cis content of about 96%.
The composition preferably contains from about 30 to about 100 parts per 100 parts of total polymer (phr) of silica. Preferably it also contains from about 25 to about 50 parts per 100 parts of total polymer (phr) of aromatic oil, selected from those known in rubber processing.
As stated above, the silica particles are hydrophobicized. A preferred method for hydrophobicizing silica particles is described in copending International patent application PCT/CA98/00499, the contents of which are hereby incorporated by reference. This preferred process comprises the steps of:
(a) contacting the particles with a compound of Formula I:
or an acid addition or quaternary ammonium salt thereof, in which:
at least one of R
1
, R
2
and R
3
, preferably two of R
1
, R
2
and R
3
and most preferably R
1
, R
2
and R
3
are hydroxyl or hydrolysable groups;
R
4
is a divalent group that is resistant to hydrolysis at the Si—R
4
bond;
R
5
is selected from the group comprising: hydrogen; a C
1-40
alkyl; a C
2-40
mono-, di- or tri-unsaturated alkenyl group; a C
6
-C
40
aryl
Bayer Inc.
Cheung Noland J.
Cheung William K
Gil Joseph C.
Seng Jennifer R.
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