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
1998-01-14
2001-02-06
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S233000, C525S236000
Reexamination Certificate
active
06184296
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to mixtures prepared from rubbers containing C═C double bonds and rubber gels modified by chemicals having a vulcanizing action and to vulcanizates produced therefrom. The vulcanizates exhibit an unusually high reinforcing action as a filler in rubber vulcanisates and unusually low dynamic damping at relatively elevated temperatures and are thus particularly suitable for the production of low rolling resistance motor vehicle tire treads.
2. Description of the Prior Art
Many methods for reducing the rolling resistance of tires have been described in the literature, including inter alia the use of polychloroprene gels (EP-A 405 216) and polybutadiene gels (DE-A 42 20 563) in tire treads made from rubbers containing C═C double bonds. The disadvantage of using these two rubber gels as a filler in rubber vulcanizates is their relatively low reinforcing action in comparison with carbon black. The sulphur-vulcanized rubber gels described in British patent GB 1 078 400 as processing auxiliaries exhibit no reinforcing properties and are thus not suitable for replacing filler in tire treads.
SUMMARY OF THE INVENTION
It has now been found that specific subsequently chemically modified rubber gels in vulcanizates prepared from rubbers containing C═C double bonds have a surprisingly strong reinforcing action as a filler and are thus better suited, for example, for the production of low rolling resistance tires than the original, unmodified rubber gels.
The present invention accordingly provides mixtures prepared from at least one rubber gel modified with compounds containing sulphur which are reactive towards C═C double bonds (chemicals having a vulcanising action) (A) and at least one rubber containing double bonds (B), wherein the proportion of modified rubber gel is 1 to 100 parts by weight, preferably 5 to 75 parts by weight, relative to 100 parts by weight of rubber containing C═C double bonds, optionally together with further fillers and rubber auxiliary substances.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Rubber gels are taken to mean microgels (A) produced by crosslinking
BR
polybutadiene
ABR
butadiene/acrylic acid C
1-4
alkyl ester copolymers
IR
polyisoprene
NR
natural rubber
SBR
styrene/butadiene copolymers having styrene contents of 1 to
60, preferably 2 to 50 wt. %
XSBR
styrene/butadiene copolymers and graft polymers with
further unsaturated polar monomers, such as acrylic acid,
methacrylic acid, acrylamide, methacrylamide, N-meth-
oxymethylmethacrylamide, N-acetoxymethylmethacrylamide,
acrylonitrile, hydroxyethyl acrylate and/or hydroxyethyl
methacrylate having styrene contents of 2 to 50 wt. % and
copolymerised polar monomer contents of 1 to 20 wt. %,
IIR
isobutylene/isoprene copolymers having isoprene contents of
0.5 to 10 wt. %
BRIIR
brominated isobutylene/isoprene copolymers having bromine
contents of 0.1 to 10 wt. %
ClIIR
chlorinated isobutylene/isoprene copolymers having chlorine
contents of 0.1 to 10 wt. %
NBR
butadiene/acrylonitrile copolymers having acrylonitrile
contents of 5 to 60, preferably 10 to 50 wt. %
HNBR
partially hydrogenated NBR rubber, in which up to 98.5% of
the double bonds are hydrogenated
EPDM
ethylene/propylene/diene copolymers
or mixtures thereof.
The rubber gels surface-modified with chemicals having a vulcanizing action have particle diameters of 5 to 2000 nm, preferably of 20 to 600 nm (DVN value to DIN 53 206) and swelling indices (Q
i
) in toluene of 1 to 15, preferably of 1 to 10. The swelling index is calculated from the weight of the gel containing solvent (after centrifugation at 20000 rpm) and the weight of the dry gel:
Q
i
=wet weight of gel/dry weight of gel.
The swelling index is determined by swelling, for example, 250 mg of gel in 25 ml of toluene for 24 hours with shaking. The gel is centrifuged out from the solvent and weighed and then dried to constant weight at 70 C and reweighed.
The uncrosslinked rubber starting products are preferably produced by emulsion polymerization, cf in this connection, for example, I. Franta,
Elastomers and Rubber Compounding Materials
, Elsevier, Amsterdam 1989, pp. 88-92.
Crosslinking to produce the rubber gels proceeds in the latex state and may proceed, on the one hand, during polymerization by continuing polymerization to high conversions or, in the monomer feed process, by polymerization at elevated internal conversions or be performed after polymerization by post-crosslinking or also by a combination of both processes. Production by polymerization in the absence of chain-transfer agents is also possible.
The rubber may also be crosslinked by copolymerization with polyfunctional compounds having a crosslinking action. Preferred polyfunctional comonomers are compounds having at least two, preferably 2 to 4, copolymerisable C═C double bonds, such as diisopropenylbenzene, divinylbenzene, divinyl ether, divinyl sulphone, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, 1,2-polybutadiene, N,N′-m-phenylenemaleimide and/or triallyl trimellitate. Further compounds which may be considered are: the acrylates and methacrylates of polyhydric, preferably di- to tetrahydric, C
2
to C
10
alcohols, such as ethylene glycol, 1,2-propanediol, butanediol, hexanediol, polyethylene glycol having 2 to 20, preferably 2 to 8 oxyethylene units, neopentyl glycol, bisphenol A, glycerol, trimethylolpropane, pentaerythritol, sorbitol and unsaturated polyesters prepared from aliphatic di- and polyols together with maleic acid, fumaric acid and/or itaconic acid.
The rubbers may also be crosslinked in the latex form to yield rubber gels by post-crosslinking with chemicals having a crosslinking action. Suitable chemicals having a crosslinking action are, for example, organic peroxides, for example dicumyl peroxide, t-butylcumyl peroxide, bis-(t-butylperoxyisopropyl)benzene, di-t-butyl peroxide, 2,5-dimethylhexane-2,5-dihydroperoxide, 2,5 -dimethylhex-3 -yne-2,5-dihydroperoxide, dibenzoyl peroxide, bis-(2,4-dichlorobenzoyl) peroxide, t-butyl perbenzoate, as well as organic azo compounds, such as azobisiso-butyronitrile and azobiscyclohexanenitrile, as well as di- and polymercapto compounds, such as dimercaptoethane, 1,6-dimercaptohexane, 1,3,5-trimercapto-triazine and mercapto-terminated polysulphide rubbers, such as mercapto-terminated reaction products of bis-chloroethyl formal with sodium polysulphide.
The optimum temperature for performing post-crosslinking is naturally dependent upon the reactivity of the crosslinking agent and it may be performed at temperatures from room temperature to approx. 170 C, optionally under elevated pressure; c.f. in this connection,
Houben-Weyl, Methoden der organischen Chemie
, 4
th
edition, volume 14/2, page 848. Peroxides are particularly preferred cross-linking agents.
Particle enlargement by agglomeration may optionally also be performed before, during or after post-crosslinking in the latex form.
Rubbers which were produced in organic solvents may also be used as starting products for the production of the rubber gels. In this case, it is advisable to emulsify the solution of the rubber in water, optionally with the assistance of an emulsifier, and subsequently to crosslink the resultant emulsion with suitable crosslinking agents before or after removal of the organic solvent. Suitable crosslinking agents are those mentioned above.
The phrase “modification with chemicals having a vulcanising action” is taken to mean the chemical reaction of the already crosslinked rubber particles with chemicals containing sulphur which are reactive towards C═C double bonds.
These are in particular those compounds by means of which reactive groups containing sulphur, such as for example mercapto, dithiocarbamate, polysulphide, xanthogenate, thiobenzothiazole and/or dithiophosphoric acid groups, may be chemically bonded to the rubber particles.
Particularly preferred modification reactions involve the reaction of the already crosslinked rubber particles with:
element
Eisele Ulrich
Jeske Winfried
Obrecht Werner
Scholl Thomas
Bayer AG
Connolly Bove & Lodge & Hutz LLP
Henderson Christopher
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