Preparation of elastomer reinforced with in situ formed...

Details Preparation of elastomer reinforced with in situ formed... Preparation of elastomer reinforced with in situ formed...

2000-03-09

2002-03-19

Moore, Margaret G. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C428S446000, C152S209100, C156S114000, C524S492000, C524S264000, C524S262000, C524S265000

Reexamination Certificate

active

06359034

ABSTRACT:

FIELD
This invention relates to preparation of an elastomer which contains a dispersion of silica reinforcement by forming a silica reinforcement in situ within an unvulcanized elastomer host, the resulting elastomer/filler composite and tire having component which contains such reinforced elastomer. The invention includes a rubber composition of at least two elastomers wherein one of said elastomers is a pre-formed composite of elastomer/in situ formed silica reinforcement. A tire having a component of such rubber composition, particularly a tire tread, is specifically contemplated.
BACKGROUND OF THE INVENTION
Elastomers are conventionally reinforced with particulate reinforcing fillers such as, for example, carbon black and sometimes precipitated silica.
It is sometimes difficult to obtain an adequate, homogeneous dispersion of silica in the rubber composition, by conventionally blending amorphous silica with unvulcanized rubber under high shear mixing conditions. Such difficulty may be, for example, because of a typically large difference in polarity and hydrophobicity between conjugated diene-based elastomers and precipitated silica, the silica may tend to agglomerate, or clump, together to form small domains of silica aggregates within the elastomer instead of widely disperses silica aggregates, or particles.
Accordingly, it is sometimes desired to more effectively create a homogeneous dispersion of the silica particles within the rubber composition.
Historically, alternate methods of creating a dispersion of silica in various elastomers has been suggested without simply dry blending precipitated silica and rubber under high shear and relatively high temperature conditions.
Historically, dispersing of silica in polysiloxane polymers such as poly(dimethylsiloxane), or (PDMS), elastomer(s) has been suggested by in-situ formation of silica from a base-catalyzed sol-gel conversion of tetraethoxysilane (TEOS). For example see “Precipitation of Silica-Titania Mixed-Oxide Fillers Into Poly(dimethylsiloxane) Networks” by J. Wen and J. Mark; Rubber Chem and Tech, (1994), volume 67, No.5, (pages 806-819).
Historically, a process of preparing rubber products has been suggested by mixing the TEOS with a solution of unvulcanized rubber in an organic solvent and subjecting it to a sol-gel condensation reaction to provide a finely powdered, spherically shaped, silica within the rubber. For example, see Japanese patent application publication 93/02152.
Historically, a composition has been suggested which comprises a rubber and globular silica made by a sol-gel method and having an average particle diameter of 10-30 microns and specific surface area of 400-700 square meters per gram. The composition is suggested for use in a flap of a tire. For example, see Japanese patent application publication 6145429.
Historically, a tread rubber composition has been proposed as a composition of rubber and spherical silica prepared by a sol-gel transformation. For example, see Japanese patent application publication 6116440 and corresponding Japanese patent publication 2591569.
Historically, an in-situ formation of silica from a sol gel reaction of TEOS in an organic solution of styrene/butadiene rubber, onto which a bis(3-triethoxysilylpropyl) tetrasulfide has been previously grafted to form triethoxysilyl groups, has been reported. (“The Effect of Bis(3-triethoxysilylpropyl) Tetrasulfide on Silica Reinforcement of Styrene-Butadiene Rubber” by Hashim, et al, in Rubber Chem & Tech, 1998, Volume 71, pages 289-299).
However, it is envisioned herein that it would be advantageous to create a relatively homogeneous particulate silica dispersion within an elastomer of a very small silica particle size which is not predominately spherical in shape.
In the description of this invention, the term “phr” where used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber, or elastomer”.
In the description of this invention, the terms “rubber” and “elastomer” if used herein, may be used interchangeably, unless otherwise prescribed. The terms “rubber composition”, “compounded rubber” and “rubber compound”, if used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with this invention, a method is provided of preparing an elastomer/silica composite as a dispersion of a filler formed in-situ within an elastomer host via a condensation reaction of TEOS and an additional organosilane, by
(A) blending with an organic solvent solution of at least one diene hydrocarbon based elastomer containing 100 parts by weight (phr) of said elastomer;
(1) an organic solvent solution of said TEOS containing about 0.5 to about 50, alternately about 5 to about 30, phr of said TEOS;
(2) an organic solvent solution of said additional organosilane containing about 0.5 to about 25 phr of said organosilane;
(3) a catalytic amount of condensation reaction promoter for said TEOS and said additional organosilane and a sufficient amount of water to facilitate said condensation reaction, followed by
(B) recovering a composite of said elastomer and dispersion therein of an in situ formed condensation reaction product of said TEOS and additional organosilane; wherein said blending process comprises:
(1) substantially simultaneously blending said TEOS solution and said additional organosilane solution with said elastomer solution following which said condensation promoter and water are added, or
(2) first blending said TEOS solution with said elastomer solution, following which said condensation promoter and water are added and subsequently blending said additional organosilane solution therewith; wherein said additional organosilane is of the following general formula (I), (II), (III), or (IV).
(OR)
2
—Si—(R
1
—S
n
—R
1
x
—S
n
—R
1
y
—CH
3
)
2
  (I)
(OR)
2
—Si—(R—CH═CH—CH
3
)
2
  (II)
(OR)
2
—Si—(CH
2
—Z)
2
  (III)
wherein Z is selected from;
—CH═CH—CH
3
  (Z1)
 —CH
2
—CH═CH
2
  (Z2)
—CH
2
—CH
2
—C—(CH
3
)
3
,  (Z3)
or
—(CH
2
)
2
—O—(CH
2
)
2
—O—CH
2
—CH
3
  (Z4)
(OR)
3
—Si—R
1
—S
n
—R
1
—Si—(OR)
3
  (IV)
wherein R is an alkyl radical selected from at least one of methyl and ethyl radicals, preferably a methyl radical, R
1
is an alkyl radical selected from ethyl, propyl and butyl radicals, y is a value of 1 to and including 4, x is a value of 2 to and including 3, y is preferably a value of 2 to and including 3, and n is an average of 2 to and including 2.6 or of 3.5 to and including 4. Representative examples of Formulas (I) to (IV) are, for example:
(C
2
H
5
O)
2
—Si—[(CH
2
)
x
—S
n
—(CH
2
)
x
CH
3
)]
2
;  (I)
(C
2
H
5
O)
2
—Si—[(CH
2
—CH═CH—CH
3
)]
2
;  (II)
(C
2
H
5
O)
2
—Si—[(CH
2
—CH
2
—C(CH
3
)
3
]
2
  (III)(Z3)
(C
2
H
5
O)
2
—Si—[(CH
2
)
2
—O—(CH
2
)
2
—O—C
2
H
5
]
2
  (III)(Z4)
(C
2
H
5
O)
3
—Si—(CH
2
)
3
—S
n
—(CH
2
)
3
—Si—(C
2
H
5
O)
3
  (IV)
In practice, said elastomer host is preferably selected from at least one of homopolymers of conjugated dienes, copolymers of conjugated dienes, copolymers of conjugated diene with a vinyl aromatic compound, preferably selected from styrene and alpha-methylstyrene and more preferably styrene.
Significantly, where the solutions of TEOS and additional organosilane are substantially added to elastomer solution, filler is formed in situ within said elastomer host by a condensation reaction of said TEOS in combination with said additional organosilane.
This is considered herein to be significant, and a departure of simply creating a filler in situ within an elastomer host by a condensation of TEOS alone. The silane and thiasilane networks are a different created simultaneously in contract to the in situ formed reinforceme

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