The present invention relates to vulcanisates comprising hydrogenated nitrile rubber (HNBR) and at least one polycyclic aromatic hydrocarbon (PAH), and to the use thereof as belts, gaskets or hoses.

FIELD OF INVENTION

The present invention relates to vulcanisates comprising at least one vulcanised hydrogenated nitrile rubber (HNBR) and at least one polycyclic aromatic hydrocarbon (PAH). The invention further relates to uses of the vulcanisates in automotive components.

BACKGROUND OF INVENTION

Hydrogenated nitrile rubber (HNBR) is a synthetic hydrogenated rubber copolymer of acrylonitrile and butadiene. HNBR is generally resistant to oil and exhibits properties over a broad temperature range. HNBR can be used in automotive applications such as belts, gaskets and hoses.

HNBR is considered to be free of polycyclic aromatic hydrocarbons (PAH), (EMG Report June 2017, page 20, table 2).

International patent application publication No. WO 2010/012531 A1 and WO 2012/084377 A1 both disclose the use of rubber compositions for belts and hoses comprising a softener. The softener is free of polycyclic aromatics according to Directive 76/769/EEC.

International patent application publication No. WO 2011/128122 A2 discloses drive belts with a main body made of a polymeric material, for e.g. HNBR. The drive belts are free of PAH.

European patent application publication No. EP3327073 A1 discloses polymeric articles containing carbon black as a reinforcing filler or at least a pigment. The carbon black contains a high proportions of PAH.

International patent application publication No. WO 2017/217203 A1 discloses rubber compositions comprising a hydrogenated carboxyl-containing nitrile rubber (HXNBR), 0.5 to 5 phr of aminated PAH having 3 or more fused rings, e.g. 2-aminoanthracene, 1-aminopyrene, 1,6-diamino-9-pyrene and 3-amino-9-ethylcarbazole. WO 2017/217203 fails to disclose the effect of the aminated PAH on HXNBR components.

However, the HNBR vulcanisates from the prior art lack satisfactorily balanced stability of tensile stress and exhibit undesirable elongation at break. The HNBR vulcanisates from the prior art also exhibit undesirable retention of hardness due to ageing.

There is therefore a need to overcome at least some of the aforementioned problems associated with the HBNR from the prior art.

There is a need to provide HNBR vulcanisates that have an improved low hardness profile after ageing, change only moderately in terms of tensile stress and elongation at break.

SUMMARY OF INVENTION

The aforementioned problems are at least overcome by the present invention.

It has been found that, surprisingly, these problems are solved by HNBR vulcanisates comprising polycyclic aromatic hydrocarbons (PAHs) that have a low hardness and have only a moderate deterioration in tensile stress and in elongation at break on ageing.

In a first aspect the present invention relates to a vulcanisate comprising:

(a) 100 parts by weight of at least one vulcanised hydrogenated nitrile rubber (HNBR) and
(b) 1 part by weight to less than 12 parts by weight of at least one polycyclic aromatic hydrocarbon (PAH).

In a further aspect the present invention relates to a use of the vulcanisate as an automotive component in contact with an organic medium.

DETAILED DESCRIPTION

For a complete understanding of the present invention and the advantages thereof, reference is made to the following detailed description.

It should be appreciated that the various aspects and embodiments of the detailed description as disclosed herein are illustrative of the specific ways to make and use the invention and do not limit the scope of invention when taken into consideration with the claims and the detailed description. It will also be appreciated that features from different aspects and embodiments of the invention may be combined with features from different aspects and embodiments of the invention.

In a first aspect the present invention relates to a vulcanisate comprising:

(a) 100 parts by weight of at least one vulcanised hydrogenated nitrile rubber (HNBR) and
(b) 1 part by weight to less than 12 parts by weight of at least one polycyclic aromatic hydrocarbon (PAH).

Nitrile Rubbers (NBR) refers to rubber copolymers of at least one α,β-unsaturated nitrile unit and at least one conjugated diene unit. The nitrile rubbers may further comprise at least one copolymerisable monomer.

Hydrogenated nitrile rubbers (HNBR) refers to the corresponding NBR in which a degree of hydrogenation of C═C double bonds of the at least one conjugated diene.

Vulcanised hydrogenated nitrile rubber is understood to mean a HNBR that has been vulcanised by methods known in the art. Suitable vulcanisation methods are specified hereinafter.

Copolymer refers to polymers having more than one monomer unit. Terpolymers refers to polymers having three monomer units.

The HNBR has a degree of hydrogenation in a range of 50%-100%, preferably 90%-100%, more preferably 95%-100% and most preferably 99%-100%.

HNBR copolymer refers to a copolymer comprising at least one α,β-ethylenically unsaturated nitrile monomer unit, at least one conjugated diene monomer unit and further monomer units. The degree of a degree of hydrogenation of the HNBR copolymer can be as those described.

The at least one α,β-unsaturated nitrile unit can be provided by known α,β-ethylenically unsaturated nitriles, or mixtures thereof, for example (C3-C5)-α,β-ethylenically unsaturated nitrile (acrylonitrile), α-haloacrylonitrile (α-chloroacrylonitrile and α-bromoacrylonitrile), α-alkylacrylonitrile (methacrylonitrile, ethacrylonitrile). It is preferred that the at least one α,β-unsaturated nitrile unit is provided by acrylonitrile, methacrylonitrile, ethacrylonitrile or mixtures thereof. It is most preferred that the at least one α,β-unsaturated nitrile unit is provided by acrylonitrile.

An amount of the at least one α,β-ethylenically unsaturated nitrile monomer units may be in a range of 10-60 wt %, preferably 20-50 wt %, more preferably 30-45 wt %, based on a total amount of 100% by weight of all monomer units in the hydrogenated nitrile rubber (a).

The at least one conjugated diene unit can be provided by known dienes, or mixtures thereof, for example C4-C12dienes (1,3-butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-pentadiene). It is preferred that at least one conjugated diene unit is provided by 1,3-butadiene and isoprene. It is most preferred that the at least one conjugated diene unit is provided by 1,3-Butadiene.

An amount of the at least one conjugated diene units may be in a range of 40-90 wt %, preferably 50-80 wt % and more preferably 55-70 wt %, based on the total amount of 100 wt % by weight of all the monomer units in the hydrogenated nitrile rubber (a).

In a preferred embodiment, the at least one α,β-ethylenically unsaturated nitrile monomer units are provide by acrylonitrile or methacrylonitrile, more preferably from acrylonitrile and the at least one conjugated diene unit is provided by isoprene or 1,3-butadiene, more preferably from 1,3-butadiene.

The hydrogenated nitrile rubber may contain one or more further monomer units derived from copolymerizable monomers in an amount of 0-50 wt %, preferably 0.1-40 wt %, more preferably 0.5-30 wt % and most preferably 1-10 wt % by weight, based on the total amount of 100 wt % of all monomer units. In that case, the amounts of the other monomer units are reduced in a suitable manner, such that the sum total of all monomer units is always 100 wt %.

The further monomer units derived from copolymerizable monomers used may be provided by carboxyl-containing copolymerizable monomers, for example α,β-unsaturated (mono)carboxylic acids or esters thereof, α,β-unsaturated dicarboxylic acids or mono- or diesters thereof, or the corresponding anhydrides or amides thereof.

The α,β-unsaturated (mono)carboxylic acids may be selected from acrylic acid and methacrylic acid.

A preferred hydrogenated nitrile rubber according to the present invention may comprise of the following, the at least one α,β-ethylenically unsaturated nitrile monomer units are provided by acrylonitrile or methacrylonitrile, the at least one conjugated diene unit is provided by isoprene or 1,3-butadiene and the further monomer units derived from copolymerizable monomers is provided by acrylic acid or methacrylic acid.

A preferred hydrogenated nitrile rubber according to the present invention may comprise of the following, the at least one α,β-ethylenically unsaturated nitrile monomer units are provided by acrylonitrile or methacrylonitrile, more preferably from acrylonitrile, the at least one conjugated diene unit is provided by isoprene or 1,3-butadiene, more preferably from 1,3-butadiene, the further monomer units derived from copolymerizable monomers is provided by alkyl acrylates or alkyl methacrylates, preferably C1-C4-alkyl (meth)acrylate, more preferably butyl acrylate.

The further monomer units derived from copolymerizable monomers are Polyethylene Glycol (PEG) acrylate units derived from a PEG acrylate according to the general formula (I):

whereR=hydrogen or branched or unbranched C1-C20-alkyl, preferably C2-C20-Alkyl, more preferably ethyl, butyl or ethylhexyl,n=1 to 12, preferably 2 to 8, more preferably 2 to 5 and most preferably 2 or 3 andR1=hydrogen or CH3—.

These PEG acrylates can be purchased commercially, for example from Arkema under the Sartomer® trade name, from Evonik under the Visiomer® trade name or from Sigma Aldrich.

An amount of the PEG acrylate monomer units may be in a range from 0-50 wt %, preferably 15-50 wt % and more preferably 20-50 wt %, based on the total amount of 100 wt % of all the monomer units.

A preferred hydrogenated nitrile rubber according to the present invention may comprise of the following, the at least one α,β-ethylenically unsaturated nitrile monomer units are provided by acrylonitrile or methacrylonitrile, more preferably from acrylonitrile, the conjugated diene monomer unit is derived from isoprene or 1,3-butadiene, more preferably from 1,3-butadiene, and the further monomer unit is derived from PEG acrylate of the general formula (I) where n is 2 to 8, more preferably from PEG acrylate of the general formula (I) where n is 2 or 3.

A preferred hydrogenated nitrile rubber according to the present invention may comprise of the following:20-45 wt % of acrylonitrile monomer units,30-70 wt % of 1,3-butadiene monomer units10-25 wt % of PEG-2 acrylate monomer units or PEG-3 acrylate monomer units.

A preferred hydrogenated nitrile rubber according to the present invention may comprise of the following:20-45 wt % of the at least one α,β-ethylenically unsaturated nitrile monomer units, preferably acrylonitrile30-70 wt % of the at least one conjugated diene, preferably 1,3-butadiene10-25 wt % of PEG acrylate monomer unit, preferably ethoxy triethylene glycol methacrylate or butoxy diethylene glycol methacrylate.

The hydrogenated nitrile rubber typically has a polydispersity index (PDI=Mw/Mnwhere Mwis the weight-average molecular weight) in a range of 1.5-6, preferably 2-5 and more preferably 2.5-4.

The hydrogenated nitrile rubber typically has a Mooney viscosity (ML1+4@100° C.) in a range of 10-150, preferably 20-120 and more preferably of 25-100.

The hydrogenated nitrile rubber according to the present invention are manufactured according to methods known in the art. The method comprises a provision of the nitrile butly rubber components of the at least one α,β-unsaturated nitrile unit, the at least one conjugated diene unit and optionally the at least one copolymerisable monomer as mentioned above which are then polymerised to form the nitrile butyl rubber. This is followed by a hydrogenation of the corresponding nitrile butyl rubber for the hydrogenated nitrile rubber.

The NBR may be subjected to metathesis (as disclosed in WO-A-02/100941 and WO-A-02/100905) to reduce the molecular weight of the NBR prior to hydrogenation.

Polycyclic aromatic hydrocarbons (PAH) refers to fused organic aromatic rings (at least two aromatic rings). The PAH may be substituted or unsubstituted.

It is preferred that the PAH is selected from anthracene and phenanthrene.

It is further preferred that the PAH is non-aminated when the H(X)NBR comprises acidic groups, since the amines (when present) of the PAH can react with HNBR acidic groups forming amides and bring about an unwanted increase in hardness.

The vulcanisates according to the present invention have a low hardness and a moderate change in elongation at break (EB) on hot air ageing.

Where the vulcanisates according to the present invention have less than 1 part by weight of polycyclic aromatic hydrocarbons show a low hardness but a distinct deterioration in elongation at break (EB) on hot air ageing.

Where the vulcanisates according to the present invention have 12 or more parts by weight of polycyclic aromatic hydrocarbons have a moderate change in elongation at break on hot air ageing, but have high hardness. Vulcanisates with high hardness are more difficult to process and therefore not suitable for all applications.

Useful filler-activators include organic silanes, for example vinyltrimethyloxysilane, vinyldimethoxymethylsilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, N-cyclohexyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, isooctyltrimethoxysilane, isooctyltriethoxysilane, hexadecyltrimethoxysilane or (octadecyl)methyldimethoxysilane. Further filler-activators are, for example, interface-active substances such as triethanolamine or ethylene glycols with molecular weights of 74 to 10 000 g/mol. The amount of filler-activators is typically 0 to 10 parts by weight, based on 100 parts by weight of the hydrogenated nitrile rubber (a).

Useful ageing stabilizers are especially those which scavenge a minimum number of radicals in the peroxidic vulcanisation. These are especially oligomerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), styrenized diphenylamine (DDA), octylated diphenylamine (OCD), cumylated diphenylamine (CDPA), 4- and 5-methylmercaptobenzimidazole (MB2) or zinc salt of 4- and 5-methylmercaptobenzimidazole (ZMB2). In addition, it is also possible to use the known phenolic ageing stabilizers, such as sterically hindered phenols, or ageing stabilizers based on phenylenediamine. It is also possible to use combinations of the ageing stabilizers mentioned, preferably CDPA in combination with ZMB2 or MB2, more preferably CDPA with MB2.

The ageing stabilizers are typically used in amounts of 0.1 to 5 parts by weight, preferably of 0.3 to 3 parts by weight, based on 100 parts by weight of the hydrogenated nitrile rubber.

Examples of useful mould release agents include: saturated or partly unsaturated fatty acids and oleic acids or derivatives thereof (in the form of fatty acid esters, fatty acid salts, fatty alcohols or fatty acid amides), and also products applicable to the mould surface, for example products based on low molecular weight silicone compounds, products based on fluoropolymers and products based on phenolic resins.

The mould release agents are used as blend component in amounts of 0.2 to 10 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the hydrogenated nitrile rubber (a).

Reinforcement of the vulcanisates with glass strength members according to the teaching of U.S. Pat. No. 4,826,721 is also possible, as is reinforcement with aromatic polyamides (aramid).

The vulcanisates of the present invention are manufactured by vulcanisation, preferably in a shaping method, of a vulcanisable composition comprising the at least one hydrogenated nitrile rubber and at least one crosslinking agent, preferably at least one peroxidic crosslinking agent. The vulcanisation can either be effected in the presence of the at least one polycyclic aromatic hydrocarbon (b) or the at least one polycyclic aromatic hydrocarbon (b) is added after the vulcanisation/or to the vulcanisate.

The vulcanisation is preferably effected at temperatures in a range of 100-250° C., more preferably 120-250° C. and most preferably 130-250° C. For this purpose, the vulcanisable compositions are subjected to further processing with calendars, rolls or extruders. The pre-shaped mass is then vulcanised in presses, autoclaves, hot air systems or what are called automatic mat vulcanisation systems (“Auma”).

A vulcanisation time is typically 1 minute to 24 hours and preferably 2 minutes to 1 hour. Depending on the shape and size of the vulcanisates, a second vulcanisation by reheating may be necessary in order to achieve complete vulcanisation.

The vulcanisates of the present invention is a retention of low hardness and in the tensile stress and elongation at break on ageing.

In a further aspect the present invention relates to a use of the aforementioned vulcanisate as an automotive component in contact with an organic medium.

The automotive component cab be at least one of a belt, a gasket or a hose.

The organic medium is selected from at least one of an oil or a fuel.

The present invention is demonstrated by the following non-limiting examples.

Examples

Materials Used

Test Methods

The MDR (moving die rheometer) vulcanisation profile and analytical data associated therewith were measured in a Monsanto MDR 2000 rheometer in accordance with ASTM D5289-95.

Shore A hardness was measured with a durometer in accordance with ASTM-D2240-81.

Elongation at Break (EB) and Tensile Strength (TS)

Elongation at break and tensile strength of the vulcanisates are measured on S2 specimens according to DIN 53504 at room temperature.

The vulcanisable mixture was vulcanised at 180° C. for 15 min in a press.

TABLE 3Properties of the unaged vulcanisates(measured at room temperature)V1V2*V3*V4V5*V6HardnessShA636262896081M10MPa0.60.60.53.40.52M25MPa110.93.70.92.6M50MPa1.41.51.43.91.43M100MPa2.72.72.75.63.24.8M300MPa26.124.324.424.5—21.3EB%362336343428260330TSMPa313230362123

Vulcanisates V4 and V6, i.e. the vulcanisates with the highest amounts of PAH of 12 parts by weight, have very particularly high hardnesses. Such high hardnesses of more than 80 ShA are unwanted since this complicates processibility.

Vulcanisates V1, V2, V3 and V5 have an expected moderate rise in hardness, although the ultimate hardness value is still within an acceptable margin.

Vulcanisate V4, after ageing (hot air) for 21 days, completely surprisingly has an unexpected decrease in hardness. Vulcanisate V6, after ageing (hot air) for 7 days, likewise has an unexpected decrease in hardness. A decrease in hardness is particularly unfavourable since the HNBR vulcanisate becomes softer and hence loses sealing power when used as a gasket, for example, and therefore becomes unusable.

The effect of PAH values of 1 part by weight or more is that elongation at break deteriorates only moderately on ageing. Vulcanisate V1 without PAH, by contrast, has disadvantageous deteriorations in elongation at break that make practical use of such a vulcanisate impossible.

Having thus described the present invention and the advantages thereof, it should be appreciated that the various aspects and embodiments of the present invention as disclosed herein are merely illustrative of specific ways to make and use the invention.

The various aspects and embodiments of the present invention do not limit the scope of the invention when taken into consideration with the appended claims and the foregoing detailed description.

What is desired to be protected by letters patent is set forth in the following claims.