Nitrile rubbers having low emission values
View Patent ↗An improved polymerization process using a specific molecular weight regulator makes it possible to produce new nitrile rubbers featuring particularly low emission values and giving vulcanizates which have an advantageous profile of properties and which are of outstanding quality, in particular in odor-sensitive applications.
1. A vulcanizable mixture comprising at least one pros linker and a nitrile rubber comprising repeat units of at least one α,β-unsaturated nitrile monomer and at least one conjugated diene monomer, wherein the nitrile rubber has an emission quotient E according to general formula (I) of less than or equal to 0.25 mg/(kg*Mooney units)
E
=
[
volatile
constituents
]
[
Mooney
viscosity
]
×
[
nitrile
content
]
100
(
I
)
where
[volatile constituents] is the volatile constituents concentration in mg/kg of nitrile rubber determined by IDS GC-MS analysis according to VDA recommendation 278 (version September 2002) between 28.4 min and 34.0 min,
[Mooney viscosity] is the Mooney viscosity ML 1+4 at 100° C. of the nitrile rubber in Mooney units determined according to ASTM D 1646, and
[nitrile content] is the dimensionless α,β-unsaturated nitrile content in the nitrile rubber, wherein such content is determined in % by weight pursuant to DIN 53 625 according to Kjeldahl.
2. The vulcanizable mixture according to claim 1 , wherein the nitrile rubber is prepared in emulsion in the presence of tertiary nonyl mercaptan, wherein the emulsion polymerization is carried out up to a conversion of at least 60% by weight, based on the sum of the monomers.
3. The vulcanizable mixture according to claim 1 , wherein;
the nitrile rubber is prepared emulsion in the presence of tertiary nonyl mercaptan, wherein the emulsion polymerization is carried out up to a conversion of at least 60% by weight, based on the sum of the monomers;
the at least one α,β-unsaturated nitrile monomer is selected from a croup consisting of (C 3 -C 5 ) α,β-unsaturated nitriles and mixtures thereof; and
the at least one conjugated diene monomer is selected from a group consisting of (C 4 -C 6 ) conjugated diene and mixtures thereof.
4. The vulcanizable mixture according to claim 1 , wherein:
the nitrile rubber is prepared in the presence of tertiary nonyl mercaptan;
the at least one α,β-unsaturated nitrile monomer is selected from a group consisting of acrylonitrile, methacrylonitrile, ethacrylonitrile, and mixtures thereof; and
the at least one conjugated diene monomer is selected from a group consisting of 1,2-butadiene, 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, piperylene and mixtures thereof.
5. The vulcanizable mixture according to claim 1 , wherein:
the nitrile rubber is prepared in the presence of tertiary nonyl mercaptan;
the at least one α,β-unsaturated nitrile monomer is acrylonitrile; and
the at least one conjugated diene monomer is 1,3-butadiene.
6. The vulcanizable mixture according to claim 1 , further comprising one or more fillers and no, one or more additional additive(s).
7. The vulcanizable mixture according to claim 6 , wherein the one or more additional additives are selected from the group consisting of filler activators, antiozonants, ageing stabilizers, antioxidants, processing aids, extender oils, plasticizers, reinforcing materials and mould release agents.
8. A process for producing the vulcanizable mixture according to claim 1 , the process comprising mixing together the nitrile rubber, the at least one crosslinker, and optionally at least one further additive.
9. A process for producing vulcanizates, the process comprising vulcanizing the vulcanizable mixture according to claim 1 .
10. The process according to claim 9 , further comprising vulcanizing the vulcanizable mixture at a temperature of 100° C. to 200° C.
11. The process according to claim 9 , further comprising vulcanizing the vulcanizable mixture at a temperature of 120° C. to 190° C.
12. A vulcanizate comprising the nitrile rubber according to claim 1 .
13. The vulcanizate according to claim 12 , wherein the vulcanizate is a shaped article.
14. The vulcanizate according to claim 13 , wherein the vulcanizate is a drive belt, a roll covering, a seal, a cap, a stopper, a hose, a floor covering, a sealing mat or sheet, a profile or a membrane.