Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-11-10
2002-03-19
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S526000
Reexamination Certificate
active
06359045
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to vulcanizable rubber compounds, which amongst other constituents contain a styrene-butadiene rubber produced in solution and/or in emulsion, a butadiene rubber, optionally, natural rubber and/or synthetic cis-isoprene rubber, fillers, and a special vulcanizing system. The invention further relates to the use of said rubber compounds for the production of tires, particularly tire treads.
BACKGROUND OF THE INVENTION
One skilled in the art is aware that the sought-after properties of tires, such as low rolling resistance, low abrasion and high wet grip, can only be combined simultaneously with each other with difficulty, since these properties are sometimes in opposition to each other. Thus, for example, if carbon black is partly or completely replaced by silica as a filler, the rolling resistance of a tire is, in fact, reduced, but its abrasion-resistance is also reduced at the same time.
There has, therefore, been no lack of investigation aimed at reducing the rolling resistance without simultaneously reducing the abrasion-resistance during the production of tires. In order to solve this problem, namely to reduce the rolling resistance without reducing the abrasion-resistance at the same time, it is proposed in EP 0 501 227 that styrene-butadiene rubber produced in solution (S-SBR) be used in combination with a special silica and a filler activator.
Furthermore, EP 0 628 597 discloses the manner in which the rolling resistance can also be reduced, without simultaneously reducing the abrasion-resistance also, by employing a styrene-butadiene rubber which is produced in an emulsion (E-SBR) and which has been reinforced with silica and a filler activator.
EP 0 385 072 describes tire treads which exhibit an enhanced running performance and which are based on diene rubbers, the network bridges which consist of 1,2-dithioethanediyl bridges. Carbon black and silica are cited as possible fillers. Moreover, this application expressly mentions that C
2
crosslinking bridges are superior to other crosslinking bridges, such as C
6
or C
8
crosslinking bridges, particularly with regard to the extent of crosslinking achieved. It is also mentioned that the use of sulfur in addition, generally produces no advantages, since the reversion behavior is considerably impaired (see page 4, lines 11 to 13 and page 4, lines 27-28).
Furthermore, EP 0 432 417 describes a process for the production of tire treads which exhibit an enhanced running performance, which are based on polydiene rubbers and additive materials, and which employ systems of crosslinking agents which form C
2
crosslinking bridges, wherein it is mentioned, in particular, that crosslinking with additional sulfur addition, generally produces no advantages, since the reversion behavior is impaired (see page 5, lines 14-15).
Moreover, EP 0 530 590 discloses a process for producing diene rubber vulcanized materials, which apart from sulfur and mercapto accelerators, or sulphenamide accelerators, or mercapto accelerators and sulphenamide accelerators, also contain crosslinking agents which build C
6
or C
2
sulfur-containing bridges.
EP 0 385 073 describes vulcanized sidewalls of motor vehicle tires which are based on polydiene rubbers comprising C
2
to C
6
dithioalkanediyl bridges as network bridges. Vulcanized sidewalls of motor vehicle tires which are based on polydiene rubbers comprising C
2
to C
6
dithioalkanediyl bridges as network bridges are also described in EP 0 432 405. Furthermore, DE 22 56 511 and DE 22 65 382 describe the use of chemical compounds of general formula A—S—S—R—S—S—A′ for the vulcanization of rubbers, wherein R in the above formula represents an arbitrary divalent organic radical and A and A′ represent a large number of accelerator radicals, which amongst others include N-substituted thiocarbamoyl radicals. Said German patent applications describe vulcanized rubbers which comprise carbon black and silica as fillers but do not describe the combination thereof with filler activators.
However, the rubber compounds or vulcanized rubbers described in the afore-mentioned patent publications are in need of further optimization with regard to properties such as low rolling resistance, low abrasion and high wet grip, which are, particularly important in tire construction.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide vulcanizable rubber compounds for the production of tire treads which exhibit an improved abrasion-resistance before aging and which are based on styrene-butadiene rubber (SBR) which is reinforced with silicas in combination with filler activators, without the rolling resistance and the wet grip of the tire tread thereby being simultaneously impaired.
It has surprisingly been possible to achieve this object by the provision of vulcanizable rubber compounds which are based on SBR, which contain silica and filler activators, and which comprise a special crosslinking agent which provides C
6
bridges in combination with a selected amount of sulfur and defined vulcanization accelerators. It has also surprisingly been found that if S-SBR is used, the rubber compounds according to the invention exhibit a shortened time of vulcanization (increase in productivity) in addition to a processing safety which is not inferior to that of prior art rubber compounds, and that these vulcanized rubbers according to the invention have a higher rebound resilience than that of prior art vulcanizates.
DETAILED DESCRIPTION OF THE INVENTION
The present invention therefore relates to vulcanizable rubber compounds comprising
a) 20 to 90 parts by weight, preferably 40 to 85 parts by weight, of a styrene-butadiene rubber (SBR) which is produced in solution and/or in emulsion,
b) 10 to 50 parts by weight, preferably 20 to 40 parts by weight, of a butadiene rubber (BR),
c) 0 to 40 parts by weight, preferably 0 to 30 parts by weight, of natural rubber and/or of a synthetic cis-isoprene rubber (IR),
d) 40 to 90 parts by weight, preferably 60 to 90 parts by weight, of silica in combination with a filler activator,
e) customary additives, and f) a vulcanizing system comprising
i) 0.5 to 3.5 parts by weight of chemical compound (I)
(C
6
H
5
—CH
2
)
2
N—(C═S)—S—S—(CH
2
)
6
—S—S—(C═S)—N(CH
2
—C
6
H
5
)
2
(I)
ii) 0.3 to 1.5 parts by weight of sulfur,
iii) 1 to 3 parts by weight of benzothiazyl-2-cyclohexylsulphenamide (CBS) and/or N-tert.-butyl-2-benzothiazylsulphenamide (TBBS), and
iv) 0.5 to 4 parts by weight of N,N′-diphenylguanidine (DPG),
wherein the parts by weight are given with respect to 100 parts by weight rubber.
Suitable styrene-butadiene rubbers (SBR) for the rubber compounds according to the invention include an SBR which is produced in solution (S-SBR), which has a styrene content of 10 to 35 parts by weight, preferably 15 to 30 parts by weight, a vinyl content of 10 to 60 parts by weight, preferably 18 to 60 parts by weight, and a glass transition temperature (T
g
), as determined by means of DSC, from −80° to −10° C., preferably from −70° to −20° C., and/or an SBR which is produced in an emulsion (E-SBR), which has a styrene content of 15 to 45 parts by weight, preferably 20 to 40 parts by weight, a vinyl content of 10 to 18 parts by weight, and a T
g
, as determined by means of DSC, from −60° to −25° C., preferably from −50° to −30° C., wherein the above parts by weight are each given with respect to 100 parts by weight of copolymer rubber.
A suitable butadiene rubber (BR) for the rubber compounds according to the present invention is a BR with a cis-1,4 content from 30 to 100 parts by weight, preferably from 90 to 100 parts by weight, per 100 parts by weight of said rubber.
The SBR and the BR can be used in unextended or in oil-extended form. The total oil content of the rubber compound is usually between 25 and 45 parts by weight with respect to 100 parts by weight of rubber.
Suitable natural rubbers (NR) for the rubber compounds according t
Buding Hartmuth
Jeske Winfried
Weidenhaupt Hermann-Josef
Bayer Aktiengesellschaft
Cheung Noland J.
Gil Joseph C.
Lipman Bernard
LandOfFree
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