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
2002-05-22
2004-11-23
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S520000
Reexamination Certificate
active
06822050
ABSTRACT:
The present invention relates to fluoroelastomeric compositions consisting essentially of a VDF-based fluoroelastomer and a semi-crystalline fluoropolymer, having improved chemical and thermal resistance, high hardness and lower fluid permeability, in particular hydrocarbons, combined with good mechanical properties and usable in the preparation of sealing manufactured articles, in particular for the oil industry.
Specifically, the present invention relates to fluoroelastomeric compositions comprising a VDF-based fluoroelastomeric matrix which incorporates semi-crystalline fluoropolymer particles, wherein the semi-crystalline fluoropolymer is coated by a semi-crystalline fluoropolymer shell containing bromine and/or iodine in the polymer chain, said compositions characterized by improved mechanical properties combined with high hardness and improved surface aspect, free of roughnesses. Said combination of properties makes available fluoroelastomers usable in the oil drilling field, wherein the fluoroelastomer manufactured articles must resist to high pressure variations.
It is known to increase the fluoroelastomer hardness in the oil drilling field, high amounts of filler, such as carbon black, in an amount of the order of 40-60 phr, are to be added. In this way higher hardnesses are obtained, but the mechanical properties, in particular the elastic modulus/elongation at break ratio result clearly worsened, wherefore the so obtained manufactured article is more easily lacerable (lower elasticity).
By trying to replace the carbon black filler with a semi-crystalline fluoropolymer, for example polytetrafluoroethylene (PTFE) powder, there are many difficulties in its incorporation, without the possibility to prepare a homogeneous blend between the semi-crystalline fluoropolymer and yhe fluoroelastomer, in particular when the semi-crytalline fluoropolymer amount is high. Generally, to obtain a satisfactory homogeneization of the semi-crystalline fluoropolymer in the fluoroelastomer, it is necessary to use complicated technologies, using open mixers with complicated incorporation cycles, for example by heating the rolls and using several steps. Even operating with these extremely complicated technologies, the incorporation of the semi-crystalline fluoropolymer in the fluoroelastomer is not uniform and the manufactured article shows poor mechanical properties (in particular the modulus/elongation ratio) and poor reproducibility of the results, whereby there is poor reliability of the preparation process and a high number of pieces to be discarded. Besides, the final manufactured article is not homogeneous due to the poor disperdibility of the semi-crystalline fluoropolymer and therefore the hardness, even though it has an average value suitable to said applications, changes from point to point whereby the properties of the finished manufactured article are poor as above indicated and are not suitable for the use in the oil field, in particular in the oil drilling.
From the European patent application EP 1,031,606 it is known to incorporate under the latex form a semi-crystalline fluoropolymer containing iodine and/or bromine atoms, in a fluoroelastomer to improve the mechanical properties with respect to a fluoroelastomer filled with PTFE powder. The particles of the semi-crystalline fluoropolymer latex have sizes comprised between 10 and 100 nm. In said patent application it is stated that the use of a semi-crystalline fluoropolymer latex containing iodine and/or bromine allows to improve the mechanical properties with respect to the case of absence of iodine and/or bromine. In the Examples the introduction of iodine atoms by using iodinated transfer agents is reported. However, for oil drilling applications, the required hardness values of the manufactured article and the mechanical properties are not suitable. In said patent application it is stated that iodine and/or bromine deriving from comonomers in the preparation of the semi-crystalline fluoropolymer can be used. The comonomer content in the final product results lower than 2 moles per 100 moles of the other monomeric units of the semi-crystalline fluoropolymer. No Examples of compositions containing semi-crystalline fluoropolymers containing iodinated and/or brominated comonomers are reported. Tests carried out by the Applicant have shown that even operating in above way no fluoroelastomeric compositions suitable for oil drilling applications are obtained. See the comparative Examples.
The need was felt to have available fluoroelastomeric compositions having the following combination of peroperties:
improved mechanical properties, in particular improved elastic modulus/elongation at break ratio;
high hardness, homogeneous on the whole manufactured article and suitable for oil drilling applications;
improved chemical and thermal resistance;
excellent surface aspect, roughnesses free;
working easiness in equipments conventionally used in the fluoroelastomer field, without using complicated technologies for incorporation of fluoropolymer.
It would be desirable to have also said fluoroelastomeric compositions showing a lower permeability to fluids, in particular to hydrocarbons.
The Applicant has unexpectedly and surprisingly found that it is possible to obtain the combination of the above properties by using the specific compositions defined hereunder.
An object of the present invention are therefore fluoroelastomeric compositions comprising:
A) a fluoroelastomeric matrix based on vinylidene fluoride (VDF);
B) a semi-crystalline fluoropolymer, in an amount from >40% to 90% by weight based on the total of A)+B), comprising a semi-crystalline fluoropolymer core coated by a semi-crystalline fluoropolymer shell containing bromine and/or iodine in the polymer chain, the amount of brominated and/or iodinated comonomer being from >2% to 10% by moles per 100 moles of the other basic monomeric units of the semi-crystalline fluoropolymer B) core+shell;
the fluoroelastomer A) incorporates the fluoropolymer B), the fluoropolymer B) being formed by tetrafluoroethylene (TFE) homopolymers, or TFE by copolymers with one or more monomers containing at least one unsaturation of ethylene type, in an amount from 0.01% to 10% by moles, preferably from 0.05% to 7% by moles; the core and the shell of the fluoropolymer B) can be of a different composition between each other, the average sizes of the semi-crystalline fluoropolymer B) particles being from 10 to 100 nm, preferably from 10 to 60 nm.
The fluoroelastomeric compositions of the invention are obtainable by mixing the latex of the semi-crystalline fluoropolymer B) with the latex of the fluoroelastomer A) and subsequent coagulation.
Alternatively to the latex mixing, the fluoroelastomeric compositions of the invention can be obtained in the same reactor, using two subsequent steps: in the first step the semi-crystalline fluoropolymer B) having the above nanometric sizes is polymerized, while in the second step the fluoroelastomer A) is polymerized. By operating in this way the fluoroelastomer A) covers the latex particles of semi-crystalline fluoropolymer B) allowing to obtain a very good disperdibility of the latter in the fluoroelastomer.
The semi-crystalline fluoropolymer B) amount incorporated in the fluoroelastomeric matrix is higher than 40% by weight, preferably from >40% to 80% by weight based on the total of the polymer mixture, more preferably from 45 to 70% by weight.
The semi-crystalline fluoropolymer B) particles having the above nanometric sizes are obtainable for example by polymerization in aqueous microemulsion of perfluoropolyoxy-alkylenes as described for example in European patent application 969,027 in the name of the Applicant, herein incorporated by reference. Polymerization techniques in microemulsion wherein the oil phase is formed by polymerizable unsaturated monomers can also be used, as described in U.S. Pat. Nos. 5,523,346 and 5,616,648.
The Applicant has found that in order to obtain the results of the invention it is essential that the semi-cr
Albano Margherita
Apostolo Marco
Arrigoni Stefano
Arnet Fox PLLC
Ausimont S.p.A.
Kintner Arent Fox
Nutter Nathan M.
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