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
2000-09-01
2002-04-16
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S350000
Reexamination Certificate
active
06372857
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to rubber mixtures based on microgel-containing rubbers and masked bifunctional mercaptans and to vulcanization products produced therefrom. By the addition of the masked bifunctional mercaptans to microgel-containing rubber mixtures, an improvement in the modulus level, a reduction in the DIN abrasion after over-vulcanization and a reduction in the heat build-up under dynamic stress (measured with a Goodrich flexometer) in the vulcanization products are achieved.
BACKGROUND OF THE INVENTION
The use of microgels is described in the following patent applications and patents:
EP 405,216, DE 4,220,563, GB 1,078,400, EP 432,405 and EP 432,417. The patents and Applications EP 405,216, DE 4,220,563 and GB 1,078,400 describe the use of CR, BR and NR microgels in mixtures with rubbers containing double bonds. The reinforcing effect of the microgels (modulus) is not sufficient for technical use. This manifests itself, in particular, in that high amounts of gel have to be employed to establish technically relevant modulus ranges. Over-filling of the mixtures occurs due to these high amounts of gel, as a result of which the tear strengths of the vulcanization products decrease. There was, therefore, the technical necessity of discovering measures to increase the modulus of gel-containing rubber vulcanization products of low filler content. There was also the technical necessity of reducing the DIN abrasion after over-vulcanization and of reducing the heating up under dynamic stress (heat build-up).
The use of bismercaptans in rubber compounds is described in EP 432,405 and in EP 432,417. The doctrine in these patent publications is the use of 1,2-bis(N,N-diethylthiocarbamoyldisulfido)-ethane in the preparation of rubber compounds and the resulting advantageous properties of vulcanization products with dithioethanediyl bridges for tire side walls and for tire treads. The use of masked bifunctional mercaptans for increasing the modulus of gel-containing rubber vulcanization products of low filler content is not described and not contained as the doctrine.
SUMMARY OF THE INVENTION
It has now been found that by using masked bifunctional mercaptans a surprisingly high reinforcing effect of microgel-containing vulcanization products is achieved and, as a result, a reduction in the degree of filling with gels becomes possible. A reduction in the DIN abrasion, especially under vulcanization conditions which cause an over-vulcanization, and a reduction in the heat build-up under dynamic stress is also achieved.
DETAILED DESCRIPTION OF THE INVENTION
The present invention, therefore, provides rubber mixtures of at least one rubber (A) containing double bonds, at least one rubber gel (B) and at least one masked bismercaptan (C), wherein the content of rubber (A) containing double bonds is 100 parts by wt., the content of rubber gel (B) is 5 to 150 parts by wt., preferably 20 to 100 parts by wt., and the content of masked bifunctional mercaptan (C) is 0.1 to 10 parts by wt., preferably 0.5 to 7 parts by wt., and optionally fillers and rubber auxiliaries.
Rubber containing double bonds is understood as meaning the rubbers called R rubbers according to DIN/ISO 1629. These rubbers have a double bond in the main chain. They include, e.g.:
NR: natural rubber
SBR: styrene/butadiene rubber
BR: polybutadiene rubber
NBR: nitrile rubber
IIR: butyl rubber
HNBR: hydrogenated nitrile rubber
SNBR: styrene/butadiene/acrylonitrile rubber
CR: polychloroprene
However, rubbers containing double bonds are also to be understood as meaning rubbers which are M rubbers according to DIN/ISO 1629 and, in addition to the saturated main chain, contain double bonds in side chains. These include, e.g., EPDM.
Rubber gel (B) is understood as meaning rubber particles (microgels) which are obtained by crosslinking the following rubbers:
BR: polybutadiene,
ABR: butadiene/acrylic acid C
1-4
alkyl ester copolymers,
IR: polyisoprene,
SBR: styrene/butadiene copolymers with styrene contents of 1-60, preferably 2 to 50 percent by weight,
X-SBR: carboxylated styrene/butadiene copolymers,
FKM: fluorinated rubber,
ACM: acrylate rubber,
NR: natural rubber,
NBR: polybutadiene/acrylonitrile copolymers with acrylonitrile contents of 5 to 60, preferably 10 to 50 percent by weight,
X-NBR: carboxylated nitrile rubbers,
CR: polychloroprene,
IIR: isobutylene/isoprene copolymers with isoprene contents of 0.5 to 10 percent by weight,
BIIR: brominated isobutylene/isoprene copolymers with bromine contents of 0.1 to 10 percent by weight,
CIIR: chlorinated isobutylene/isoprene copolymers with bromine contents of 0.1 to 10 percent by weight,
HNBR: partly 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.
Crosslinking of rubbers containing double bonds is preferred, in particular: CR, NR, NBR, BR and SBR.
The microgels have particle diameters of 5 to 1,000 nm, preferably 20 to 600 nm (DVN value according to DIN 53206). Because of their crosslinking, they are insoluble and are swellable in suitable swelling agents, such as, e.g., toluene. The swelling indices of the microgels (Q
i
) in toluene are 1 to 15, preferably 1 to 10. The swelling index is calculated from the weight of the solvent-containing gel (after centrifugation at 20,000 rpm) and the weight of the dry gel:
Q
i
=wet weight of the gel/dry weight of the gel.
To determine the swelling index, 250 mg gel are allowed to swell in 25 ml toluene for 24 h, while shaking. The gel is centrifuged off and weighed and is then dried to constant weight at 70° C. and weighed again.
The non-crosslinked rubber starting products can be prepared by emulsion polymerization and solution polymerization.
Naturally occurring latices, such as natural rubber latex, can also be employed.
The following monomers which can be polymerized by free radicals are employed in the preparation of microgels by emulsion polymerization: butadiene, styrene, acrylonitrile, isoprene, esters of acrylic and methacrylic acid, tetrafluoroethylene, vinylidene fluoride, hexafluoropropene, 2-chlorobutadiene, 2,3-dichlorobutadiene and carboxylic acids containing double bonds, such as acrylic acid, methacrylic acid, maleic acid and itaconic acid, hydroxy compounds containing double bonds, such as hydroxyethyl methacrylate, hydroxyethyl acrylate and hydroxybutyl methacrylate, or epoxides containing double bonds, such as glycidyl methacrylate or glycidyl acrylate. The crosslinking of the rubber gel can be achieved directly during the emulsion polymerization by copolymerization with multifunctional compounds having a crosslinking action. Preferred multifunctional comonomers are compounds with at least two, preferably 2 to 4 copolymerizable C═C double bonds, such as diisopropenylbenzene, divinylbenzene, divinyl ether, divinyl sulfone, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, 1,2-polybutadiene, N,N′-m-phenylenemaleimide, 2,4-toluylenebis-(maleimide) and/or triallyl trimellitate. Compounds, which are moreover possible, are the acrylates and methacrylates of polyhydric, preferably 2- to 4-hydric C
2
to C
10
alcohols, such as ethylene glycol, propanediol-1,2, butanediol, hexanediol, polyethylene glycol with 2 to 20, preferably 2 to 8 oxyethylene units, neopentylglycol, bisphenol A, glycerol, trimethylolpropane, pentaerythritol, sorbitol with unsaturated polyesters from aliphatic di- and polyols and maleic acid, fumaric acid and/or itaconic acid.
The crosslinking to rubber gels during the emulsion polymerization can also take place by continuing the polymerization up to high conversions, or in the monomer feed process by polymerization at high internal conversions. Another possibility is also that of carrying out the emulsion polymerization in the absence of regulators.
For crosslinking of non-crossli
Jeske Winfried
Obrecht Werner
Bayer Aktiengesellschaft
Cheung Noland J.
Gil Joseph C.
Michl Paul R.
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