Gel-containing rubber mixtures with inorganic peroxides

Details Gel-containing rubber mixtures with inorganic peroxides Gel-containing rubber mixtures with inorganic peroxides

2001-11-09

2003-06-17

Nutter, Nathan M. (Department: 1711)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

Reexamination Certificate

active

06579945

ABSTRACT:

FIELD OF THE INVENTION
The present invention provides rubber mixtures which contain crosslinked rubber particles (so-called rubber gels) and also metal peroxides in addition to the conventional mixture constituents, which are characterised in the uncrosslinked state by good processability (compound viscosity—ML 1+4/100(C.) and in the vulcanized state by improved mechanical properties in particular with regard to the product of the modulus at 100% extension and the elongation at break (S
100
×D) and also by improved tensile strengths. In addition, vulcanizates prepared from rubber mixtures according to the present invention have a relatively low density, which has an advantageous effect on the weight of the rubber molded items produced from the vulcanizates, in particular in the case of tires and tire parts.
BACKGROUND OF THE INVENTION
It is known that rubber mixtures of uncrosslinked rubbers and crosslinked rubber particles (rubber gels) have a low specific weight and low mixing viscosity and that vulcanizates are produced during vulcanization with conventional vulcanizing agents (e.g. sulfur vulcanization) which have a high rebound resilience at 70° C. and therefore, exhibit low damping under normal conditions of use.
In this connection, reference is made, for example, to U.S. Pat. Nos. 5,124,408, 5,395,891, DE-A 197 01 488.7, DE-A 197 01 487.9, DE-A 199 29 347.3, DE-A 199 39 865.8, DE-A 199 42 620.1 and DE-A 19701487.
For industrial use, the mechanical properties of gel-containing rubber vulcanizates are inadequate, in particular due to poor tear strengths and the defective reinforcing effects of microgels. In particular, an improvement in the product S
100
×D, modulus at 100% extension (S
100
) and elongation at break (D), and in the tear strength (F) are required. These improvements should be achieved without causing any significant worsening of the advantageous mixture viscosities of the unvulcanized rubber mixtures.
The use of metal peroxides in combination with sulfur for crosslinking carboxyl group-containing rubbers such as e.g. carboxylated nitrile rubber is disclosed in U.S. Pat. No. 3,403,136. In this patent, the improvement in mechanical properties of gel-containing rubber compounds, however, is not disclosed.
From U.S. Pat. No. 2,765,018 it is known to react butyl rubber with inorganic peroxides. According to the disclosure in this patent, only incomplete vulcanization (“partially cured”) is achieved. It cannot be gathered from this patent how the mechanical properties of fully crosslinked gel-containing rubber compounds can be improved.
According to EP-A 313 917, carboxyl group-free rubbers are vulcanized with vulcanizing systems which contain sulfur and peroxides of metals. The crosslinking of compounds which contain rubber particles is not disclosed.
Thus, there is an industrial-scale need to find measures to increase the general mechanical properties of gel-containing rubber vulcanizates, in particular the tear strength and the product of the modulus at 100% extension and the elongation at break (S
100
×D), wherein the compound viscosities of the unvulcanized mixtures are not significantly worsened by these measures.
SUMMARY OF THE INVENTION
Therefore the present invention provides rubber mixtures of at least one double bond-containing rubber (A), at least one rubber gel (B) and at least one metal peroxide (C), wherein the double bond-containing rubber (A) is present in amounts of 100 parts by wt., the rubber gel (B) is present in amounts of 10 to 150, preferably 20 to 120, parts by wt. and the peroxide (C) is present in amounts of 0.1 to 30, preferably 0.5 to 15, parts by wt.
DETAILED DESCRIPTION OF THE INVENTION
Rubber mixtures according to the present invention may obviously also contain known rubber fillers and rubber auxiliary substances as well as crosslinkers.
Constituent (A) in rubber mixtures according to the present invention are double bond-containing rubbers which are called R rubbers according to DIN/ISO 1629. These rubbers have a double bond in the main chain. The following, for example, are included among these:
NR:
natural rubber
IR:
polyisoprene
SBR:
styrene/butadiene rubber
BR:
polybutadiene rubber
SIBR:
styrene/isoprene/butadiene rubber
NBR:
nitrile rubber
IIR:
butyl rubber
BIIR:
brominated isobutylene/isoprene copolymers with bromine
contents of 0.1-10 wt. %
CIIR:
chlorinated isobutylene/isoprene copolymers with chlorine
contents of 0.1-10 wt. %
HNBR:
hydrogenated or partially hydrogenated nitrile rubber
SNBR:
styrene/butadiene/acrylonitrile rubber
CR:
polychloroprene
ENR:
epoxidized natural rubbers or mixtures thereof
X-NBR:
carboxylated nitrile rubber
X-SBR:
carboxylated styrene/butadiene copolymers.
NR, BR, SBR and SIBR are preferred.
However, double bond-containing rubbers are also understood to be those rubbers which are called M rubbers according to DIN/ISO 1629 and have, apart from a saturated main chain, double bonds in the side chains. EPDM, for example, is included here.
Double bond-containing rubbers of the types mentioned above to be used in rubber mixtures according to the present invention may obviously be modified by those functional groups which react with zinc peroxide and which enable improvement of the linkage of crosslinked rubber particles to the surrounding rubber matrix in the vulcanized state.
Preferred uncrosstinked rubbers are those which are functionalized by hydroxyl, carboxyl, amino, amide and/or epoxide groups. The introduction of functional groups may take place directly during polymerization, by copolymerization with suitable comonomers, or after polymerization by polymer modification.
The introduction of such functional groups by polymer modification is known and is described, for example, in M. L. Hallensleben “Chemisch modifizierte Polymere” in Houben-Weyl Methoden der Organischen Chemie, 4th edition, “Makromolekulare Stoffe”, part 1-3; Georg Thieme Verlag Stuttgart, N.Y., 1987; p.1994-2024, DE-A 2 653 144, EP-A 464 478, EP-A 806 452 and DE-A 198 32 459.6.
The amount of functional groups in the rubbers is generally 0.05 to 25 wt. %, preferably 0.1 to 10 wt. %.
Constituent (B) in rubber mixtures according to the present invention are crosslinked rubber particles, so-called rubber gels or microgels, which are obtained by appropriate crosslinking of the following rubbers:
NR:
natural rubber,
BR:
polybutadiene,
ABR:
butadiene/C
1-4
alkyl acrylate copolymers,
IR:
polyisoprene,
SBR:
styrene/butadiene copolymers with styrene contents of
1-60, preferably 5-50 wt. %,
SIBR:
styrene/isoprene/butadiene rubber,
X-SBR:
carboxylated styrene/butadiene copolymers,
FKM:
fluorinated rubbers,
ACM:
acrylate rubbers,
NBR:
polybutadiene/acrylonitrile copolymers with acrylonitrile
contents of −60, preferably 10-50 wt. %,
X-NBR:
carboxylated nitrile rubbers,
ENR:
epoxidized natural rubber,
CR:
polychloroprene,
IIR:
isobutylene/isoprene copolymers with isoprene contents
of 0.5-10 wt. %,
BIIR:
brominated isobutylene/isoprene copolymers with
bromine contents of 0.1-10 wt. %,
CIIR:
chlorinated isobutylene/isoprene copolymers with
chlorine contents of 0.1-10 wt. %,
HNBR:
partially and fully hydrogenated nitrile rubbers,
EPM:
ethylene/propylene copolymers,
EPDM:
ethylene/propylene/diene terpolymers,
EAM:
ethylene/acrylate copolymers,
EVM:
ethylene/vinylacetate copolymers,
CO and ECO:
epichlorhydrin rubbers,
Q:
silicone rubbers,
AU:
polyesterurethane polymers,
EU:
polyetherurethane polymers.
BR, NR, SBR, NBR and CR are preferred.
Rubber particles to be used according to the present invention normally have particle diameters of 5 to 1000 nm, preferably 10 to 600 nm (data relating to diameter in accordance with DIN 53 206).
Due to the crosslinking, they are (almost) insoluble and are swellable in suitable precipitating agents, e.g. toluene. The (insoluble) gel fraction of the rubber particles generally amounts to 80 to 100 wt. %, preferably 90 to 100 wt. %. The swelling index of the rubber particles (Ql) in toluene is about 1 to 15, preferably 1 to 10.
The swelling index Ql is defined as:
Ql
=
wet
⁢
&e

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