Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-08-16
2003-09-16
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...
C526S335000, C526S348200, C526S348500, C526S348600
Reexamination Certificate
active
06620866
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to agglomerated rubber gels, to rubber mixtures produced therefrom and to the use thereof. The vulcanizates containing agglomerated rubber gels are distinguished, in comparison with compounds that contain the corresponding non-agglomerated gels, by improved mechanical properties with at least an equivalent damping behavior. In particular, rubber mixtures containing “structured” rubber gels, as well as compounds based on silica-containing agglomerated rubber gels which have been activated by sulfur-containing silicon compounds, exhibit especially advantageous mechanical properties.
BACKGROUND OF THE INVENTION
The use of microgels in rubber compounds is described in the following patent applications and patents: EP-A 405,216, DE-A 4,220,563, GB-B 1,078,400 and EP-A 854,171 EP 432,405 and EP 432,417. Patents/patent applications EP-A 405,216, DE-A 4,220,563 and GB-B 1,078,400 describe the use of CR, BR and NR microgels for mixtures with double-bond-containing rubbers and for the production of the corresponding vulcanizates. The vulcanizates are suitable especially for the production of tire treads, since they exhibit a high rebound resilience at 70° C. and hence low rolling resistance, and a low rebound resilience at 23° C. and hence a high wet-skid resistance. In particular, the large difference between the rebound resilience at 70° C. and that at 23° C. is characteristic of vulcanizates containing microgels. For industrial use in tire treads, however, the mechanical properties of microgel-containing vulcanizates are inadequate. Deficiencies exist especially in the level of mechanical vulcanizate properties. There is a need to improve the product from the tensile stress at 300% elongation and elongation at tear as well as the abrasion resistance.
Sulfur-containing organosilicon compounds play a particular part in the activation of silica-containing rubber mixtures. The following patent specifications are mentioned by way of examples: U.S. Pat. No. 3,873,489 (Degussa), U.S. Pat. No. 4,709,065 (Shin-Etsu) and U.S. Pat. No. 5,227,425 (Michelin), EP-B 670,347, EP-A 753,549, EP-A 864,608.
These patents do not teach the improvement of the mechanical properties of vulcanizates based on rubber gels by the use of agglomerated rubber gels or rubber gels co-agglomerated with inorganic fillers, such as silica.
SUMMARY OF THE INVENTION
The technical object was, therefore, to improve the level of mechanical values (tensile stress (300%×elongation at tear)) as well as the abrasion resistance of microgel-containing rubber vulcanizates, without impairing the difference between the rebound resilience at 70° C. and at 23° C.
It has now been found that it is possible to improve the reinforcing effect of rubber gels in vulcanizates if the rubber gels are used in agglomerated form. The reinforcing effect of the agglomerated rubber gels is especially pronounced if the particles are unable to assume the thermodynamically most advantageous spherical form after the agglomeration, that is to say if the agglomerated particles have a certain structure. In particular, the use of rubber gels co-agglomerated with inorganic fillers, such as silica, is especially advantageous. The reinforcing effect of the silica-containing rubber gels is improved further because a sulfur-containing organosilicon compound is additionally used in the compounding.
Accordingly, the present invention provides rubber mixtures containing at least one agglomerated rubber gel (A), at least one double-bond-containing rubber (B), and at least one sulfur-containing organosilicon compound (C), the amount of double-bond-containing rubber (B) being 100 parts by weight, the amount of rubber gel (A) being from 1 to 150 parts by weight, preferably from 10 to 100 parts by weight, and the amount of organosilicon sulfur compound (C) being from 0.2 to 20 parts by weight, preferably from 1 to 10 parts by weight, as well as further rubber auxiliary substances and, optionally, further fillers.
DETAILED DESCRIPTION OF THE INVENTION
As discussed above, the present invention relates to rubber mixtures containing at least one agglomerated rubber gel (A), at least one double-bond-containing rubber (B), and at least one sulfur-containing organosilicon compound (C), the amount of double-bond-containing rubber (B) being 100 parts by weight, the amount of rubber gel (A) being from 1 to 150 parts by weight, preferably from 10 to 100 parts by weight, and the amount of organosilicon sulfur compound (C) being from 0.2 to 20 parts by weight, preferably from 1 to 10 parts by weight, as well as further rubber auxiliary substances and, optionally, further fillers.
Agglomerated rubber gels (A) are to be understood as being rubber gels having particle diameters of from 5 to 5000 nm. They have a broad particle size distribution, characterized by the difference between the d
80
and d
10
values, which is greater than 25 nm. The characteristic diameters d
10
and d
80
are the diameters below which 10 wt. % and 80 wt. %, respectively, of the particles lie. The particle size distributions are determined by means of ultracentrifugation according to H. Lange, “Schnelle Dichtegradienten-zentrifugation dispergierter Teilchen”, Colloid & Polymer Sci. 258, 1077-1085 (1980) or H. G. Müller, “Automated determination of particle-size distributions of dispersions by analytical ultracentrifugation”, Colloid & Polymer Science 267: 113-116 (1989).
In cases where the agglomerated particles are not in spherical form after the agglomeration and have “structure”, these can be identified by suitable methods, for example by electron microscopy.
Due to their crosslinking, the rubber gels are insoluble and are swellable in suitable swelling agents, such as toluene. The swelling indices of the microgels (Q
i
) in toluene are from 1 to 15, preferably from 1 to 10. The swelling index is calculated from the weight of the gel containing solvent (after centrifugation at 20,000 rpm) and the weight of the dry gel:
Q
1
=wet weight of the gel/dry weight of the gel.
In order to determine the swelling index, 250 mg of gel, for example, are allowed to swell in 25 ml of toluene for 24 hours, with shaking. The gel is removed by centrifugation and weighed and is then dried at 70° C. until a constant weight is reached and then weighed again.
The agglomerated rubber gels may also contain inorganic fillers, especially silica, in amounts of approximately from 3 to 80 wt. %, preferably from 5 to 50 wt. %, rubber gels containing fillers having lower swelling indices due to their filler content. If, in those cases, the swelling indices are related to the pure rubber component of the gel containing filler, then they are within the range indicated above.
For the production of the rubber gels, the following rubbers are used:
BR:
polybutadiene,
ABR:
butadiene/acrylic acid C
1
-C
4
-alkyl ester copolymers,
IR:
polyisoprene,
SBR:
styrene-butadiene copolymers having styrene contents of
from 1 to 60 wt. %, preferably from 2 to 50 wt. %,
X-SBR:
carboxylated styrene-butadiene copolymers,
FKM:
fluorine rubber,
ACM:
acrylate rubber,
NBR:
polybutadiene-acrylonitrile copolymers having acrylonitrile
contents of from 5 to 60 wt. %, preferably from 10 to 50 wt. %,
X-NBR:
carboxylated nitrile rubbers,
CR:
polychloroprene,
IIR:
isobutylene/isoprene copolymers having isoprene contents of
from 0.5 to 10 wt. %,
BIIR:
brominated isobutylene/isoprene copolymers having bromine
contents of from 0.1 to 10 wt. %,
CIIR:
chlorinated isobutylene/isoprene copolymers having chlorine
contents of from 0.1 to 10 wt. %,
HNBR:
partially and completely hydrogenated nitrile rubbers,
EPDM:
ethylene-propylene-diene copolymers,
EAM:
ethylene/acrylate copolymers,
EVM:
ethylene/vinyl acetate copolymers,
ECO:
epichlorohydrin rubber,
Q:
silicone rubbers,
AU:
polyester urethane polymers,
EU:
polyether urethane polymers,
ENR:
epoxidized natural rubber
or mixtures thereof.
Preparation of the uncrosslinked rubber starting materials is carried out by the following methods:
1. emulsion polymerization,
2. solutio
Jeske Winfried
Obrecht Werner
Bayer Aktiengesellschaft
Cheung Noland J.
Cheung William
Gil Joseph C.
Seng Jennifer R.
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