Blends of fluorinated and acrylic elastomers

Details Blends of fluorinated and acrylic elastomers Blends of fluorinated and acrylic elastomers

2001-08-17

2003-12-02

Wu, David W. (Department: 1713)

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

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C525S070000, C525S080000, C524S461000, C524S462000, C526S343000

Reexamination Certificate

active

06656991

ABSTRACT:

The present invention relates to elastomers obtained from blends of fluorinated rubber and hydrocarbon rubber having improved mechanical properties.
Particularly, the fluorinated rubber is meant a rubber based on vinylidene fluoride (VDF) and hydrocarbon rubber is meant a hydrocarbon elastomer having at least one acrylic monomer as base monomer.
The fluorinated elastomer (FKM) performances, intended as the set of mechanical properties, compression set, thermal and chemical resistance, are notably higher than those of hydrocarbon rubbers. Such high performances of fluorinated elastomers involve however rather high costs making their use very restricted. This is due to the higher cost of the monomers and to the process technology used in their preparation.
As a consequence the users of elastomers are obliged to choose between two elastomeric families which are completely different in terms of performances and costs: fluorinated elastomers and hydrocarbon elastomers.
On one hand, there was a need to have available elastomers showing superior mechanical properties and superior properties in terms of thermal and chemical resistance compared with hydrocarbon elastomers used at present.
U.S. Pat. No. 5,902,860 describes a peroxide curable blend of hydrocarbon elastomers and fluorinated VDF-base elastomers wherein the fluororubber ranges from 5% to 75% by weight, the elastomers of said blend, that do not contain iodine and/or bromine show improved properties compared with the hydrocarbon elastomers. The Applicant has found that with these blends it is not possible to operate at high content of fluororubber since the blends are not even mouldable.
On the other hand, there was also a need to have avaible elastomers blends containing a high amount of fluororubber having a good combination of the above properties in order to cover severe applications whereby the fluororubber is over-designed.
Another important issue in the rubber industry is the shelf life of the compound which comprises the rubber and the the vulcanization ingredients mixed together. A good shelf life implies that the rheometric (viscosity) and mechanical properties of the compound do not change substantially with time. On the other way around, a compound that ages easily shows a more rapid increase with time of Mooney viscosity, changing the processing conditions with time and worsening the mechanical properties.
Another request is that the compound must not scorch.
The Applicant has now surprisingly and unexpectedly found that it is possible to obtain new elastomers, curable by peroxidic way, formed by a blend of fluoroelastomers and hydrocarbon elastomers, said blend not containing iodine and/or bromine, having improved properties.
The new elastomers, after vulcanization, show the following combination of properties:
improved mechanical and elastomeric properties,
good chemical and thermal resistance, with respect to hydrocarbon elastomers and respect to fluororubber/acrilic rubber elastomeric blends described in the prior art, in particular when the fluororubber content is the major part of the blend. Furthermore the new elastomeric compound has a long shelf life without the drawbacks above mentioned.
An object of the present invention is a compound comprising a peroxide and a curable blend consisting essentially of unsaturated-fluorinated elastomers obtained by dehydrohalogenation of fluorinated elastomers based on VDF having in the polymer chain at least 5% by moles of hydrogenated groups C
1
of the type
—CH
2
— and/or —CH
3
, and of hydrocarbon elastomers containing at least an acrylic monomer, the amount of unsaturated-fluorinated elastomer in the elastomeric blend being comprised from 1 to 99% by weight, preferably from 30 to 97% by weight, more preferably from 50 to 95% by weight, said elastomers of the blend not containing iodine and/or bromine.
The unsaturated fluoroelastomers contain —CH═CF— units and are obtained by dehydrohalogenation of fluoroelastomers based on vinylidene fluoride (VDF).
The unsaturation in the fluoroelastomer is evident by the presence of the absorbance band of the —CH═CF— unit in a FT-IR spectrum.
Examples of fluoroelastomers are VDF/hexafluoropropene (HFP) copolymers, and optionally containing tetrafluoroethylene (TFE). Other monomers can be present in the VDF-based fluoroelastomers, for example chlorotrifluoroethylene (CTFE), ethylene (E) and perfluoroalkylvinylethers with the alkyl from 1 to 4 carbon atoms, for example perfluoromethylvinylether (MVE) and perfluoropropylvinylether (PVE).
Some fluoroelastomers having the cited monomers are for example: TFE/VDF/MVE; VDF/HFP/E; E/TFE/HFP/VDF, which are well known in the art (see EP 525,685, EP 525,687 and EP 518,073 herein incorporated by reference).
As already said, the unsaturated-fluorinated elastomers of the present invention are obtained by dehydrohalogenation of fluoroelastomers characterized by containing at least 5% by moles of hydrogenated groups C
1
(having 1 carbon atom), preferably at least 15% by moles. The fluorinated elastomers such as VDF/HFP and VDF/HFP/TFE containing hydrogenated groups C
1
in amounts of at least 30% by moles are the more preferred. Said hydrocarbon groups can be determined for example by NMR analysis.
The dehydrohalogenation of the above fluoroelastomers is in brief the elimination of HX, where X is fluorine and/or chlorine, from the fluororubber backbone by a basic reagent to produce carbon-carbon unsaturation (C═C).
The dehydrohalogenation can be done: in an organic solution containing the fluoroelastomer and an organic base; in aqueous emulsion in the presence of an inorganic base such as KOH (see U.S. Pat No. 5,733,981); in solid fluororubber mixed with a base such as Ca(OH)
2
and in the presence of onium salts for instance quaternary ammonium or phosphonium salts, such as tetrabutylammonium hydrogensulfate (TBAHS), or quaternary aminophosphonium salts such as diphenyl-benzyl-N,N-diethyl-aminophosphonium chloride.
In the case of solid fluororubber other ingredients can be added, for example polymethylvinylether aqueous solution to promote the dehydrohalogenation.
In all cases the dehydrohalogenation rate is notably increased with temperature.
In particular the preferred dehydrohalogenation process is dehydrohalogenation of a solid fluororubber mixed with a base, preferably Ca(OH)
2
, and an onium salt at a temperature higher than 100° C., preferably higher than 150° C.
The absorbance band of —CH═CF— unsaturation in the VDF/HFP fluoroelastomer is for instance found at about 1719 cm
−1
.
The hydrocarbon elastomers of the present invention preferably do not have unsaturations, and are saturated hydrocarbon elastomers.
The Applicant has found that a later addition of dehydrohalogenating ingredients to the blend containing a saturated fluoroelastomer and a hydrocarbon elastomer leads to a compound that ages and scorches.
The acrylic monomer content in the hydrocarbon or hydrogenated elastomer is generally comprised, as percentage by moles, between 20 and 100%, preferably from 40 to 100% and more preferably from 90 to 100%. The other monomers, when present, are for example hydrocarbon monomers such as, for example, hydrogenated alpha olefins such as ethylene and propylene; vinyl esters of carboxylic acids C
2
-C
8
such as vinyl acetate, vinyl propionate, vinyl 2-ethylhexanoate; olefins with other functional groups (for example allylglycidylether).
Among the most known acrylic monomers can be cited: alkyl acrylates which include C
1
-C
8
alkyl esters of acrylic and methacrylic acids, among which preferred are methyl acrylate, ethyl acrylate (EA) and butyl acrylate (BA), ethylhexylacrylate; alkoxy-substituted alkyl acrylates wherein the alkoxy group has from 2 to 20 carbon atoms, such as for example 2-methoxyethylacrylate, 2-ethoxyethylacrylate, 2-(n-propoxy)propylacrylate and 2-(n-butoxy)ethylacrylate; acrylates and methacrylates containing chlorine (for example chloro-ethyl-acrylate) or other functional groups (for example glycidyl-methacrylate).
As representative examp

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