Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-06-11
2002-04-23
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S314000
Reexamination Certificate
active
06376586
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of polymers and the subject of the invention is compositions based on fluorinated polymer(s) and their method of preparation.
BACKGROUND OF THE INVENTION
Fluorinated homopolymers and copolymers are known for their good thermal withstand capability, their chemical resistance, especially to solvents, weatherability and resistance to radiation (UV, etc.), their impermeability to gases and to liquids, and their property of being electrical insulants. They are used in particular for the production of pipes for conveying hydrocarbons extracted from off-shore or on-shore oil deposits. The hydrocarbons are sometimes transported at high temperatures (of about 135° C.) and at a high pressure (for example 70 MPa). Severe problems therefore arise, during operation of installations, relating to the mechanical, thermal and chemical resistance of the materials employed. Other requirements are added to them before or after service: thus, during their production, their installation and/or their removal (reeling/unreeling), the pipes may be subjected to impacts and to flexural loads which they must also withstand and, sometimes, they must do so at particularly low temperatures (for example −35° C.).
In order to try to meet these short-term and long-term requirements, various types of materials have been proposed, generally comprising one or more metallic components which guarantee mechanical rigidity, for example a spiralled steel tape, as well as various layers based on polymeric compositions, which in particular provide impermeability and thermal insulation. These compositions, often based on semicrystalline fluorinated polymers, especially poly(vinylidene fluoride) (PVDF), are often plasticized in order to remedy a lack of flexibility, a low elongation at the yield point and an insufficient toughness, this having the drawback of the plasticizers being extracted relatively rapidly by the hydrocarbons transported, gradually resulting in a loss of the properties provided by the plasticization (flexibility, toughness, etc.), being accompanied in general by shrinkage phenomena and consequently limiting the lifetime of the articles based on these compositions.
In order to solve some of these problems, the optionally plasticized fluorinated polymers have been replaced by polymeric compositions comprising a PVDF homopolymer, a thermoplastic copolymer of vinylidene fluoride (VF2) and of at least one other fluorinated monomer (EP 608,939 and EP 608,940) and a plasticizer (EP 608,939). However, strict and precise control of the morphology of such blends demands the use of complex and expensive apparatus which therefore makes this technical solution not easily realisable; moreover, it is found that these blends have a limited toughness at low temperature and a poor swelling resistance, for example when in contact with hydrocarbons, and a chemical withstand capability which is inferior to that of PVDF by itself, and any plasticizer is extracted when in contact with certain chemicals.
Elastomeric particles have also been incorporated into PVDF (FR 2,592,655 and FR 2,618,791) for the purpose of absorbing the hydrocarbons and of fixing them throughout the blend, the proportion of elastomer within the blend having not to exceed 25% of the total mass. Such blends have improved toughness over PVDF alone, but their flexibility is insufficient for certain applications envisaged, especially for the transportation and/or storage of hydrocarbons, as this type of blend is not very flexible when not in direct contact with the hydrocarbons. FR 2,592,655 has described blends containing, in addition, at least 10% by weight of plasticizer, which, although they possess both the desired flexibility and the desired impact strength, sooner or later let the plasticizer exude.
Patent Application EP 0,714,944 describes compositions comprising a PVDF matrix in which are dispersed nodules of vulcanized elastomers which are optionally flexibilized by plasticizers. The multiaxial impact strength of these compositions is very good, but the amount of elastomer, 26.6 or 50 parts by weight per 100 parts by weight of PVDF 1000 (Examples 6 and 11), is so high that these compositions lack thermal and chemical stability at 150° C. In addition, these compositions have the drawback of a high permeability under pressure and a poor resistance to the rapid decompression of hot pressurized gases (“blistering”).
DESCRIPTION OF THE INVENTION
The present invention aims to solve the abovementioned technical problems and the subject of the invention is a flexible and tough composition comprising:
at least one homopolymer (A) of vinylidene fluoride (VF2) or a copolymer (A) of VF2 and of at least one other monomer copolymerizable with VF2, in which the said monomer is present in an amount of between 0 and 30 parts by weight per 100 parts by weight of VF2,
at least one elastomer B,
at least one plasticizer C,
characterized in that, on the one hand, the said composition comprises from 0.5 to 10 parts by weight of B and from 0.5 to 10 parts by weight of C per 100 parts by weight of A, with the additional condition that the sum of B and C is from 1 to 10.5 parts by weight and, on the other hand, in that the homopolymer or the copolymer of vinylidene fluoride, A, is chosen in such a way that it has a melt flow index, measured according to the ISO 1133 standard at 230° C. under a load of 5 kg, of less than 5 g/10 min and a critical modulus G
C
, at the intersection of the melt shear moduli G′ and G″ measured at 190° C., of between 5 and 22 kPa, the said composition having the following properties:
an elongation at the yield point, &egr;
y
, of greater than 11%, an elongation at break &egr;
b
of greater than 200%, an impact strength at 23° C. of greater than 50 kJ/m
2
and an impact strength at −30° C. of greater than 10 kJ/m
2
, these being measured according to the ISO 180-1982 standard, a resistance to flexural rupture on a sleeved metal tape of greater than 50%, a weight loss &Dgr;w in air at 150° C. for 1 month of less than or equal to 8% and a weight change &Dgr;p in petroleum (equal-volume mixture of cyclohexane, isooctane and xylene) at 150° C. for 1 month which is not negative (the said composition does not lose weight in petroleum).
The critical modulus G
C
is determined at 190° C. using a dynamic mechanical spectrometer, for example of the Rheometrics RMS 800 type, using a 25 mm diameter plane—plane viscometer.
Preferably, the said other monomer is present in a relative amount of between 0 and 5 parts by weight.
Preferably, the said other monomer is a fluorinated monomer.
Advantageously, B is present in a relative amount of from 0.5 to 5 parts by weight per 100 parts by weight of A.
Advantageously, C is present in a relative amount of from 0.5 to 5 parts by weight per 100 parts by weight of A.
The fluorinated polymers A of the compositions according to the invention are chosen from homopolymers or copolymers of VF2 because of their excellent chemical inertness in the presence of crude gas or petroleum and because of their high-temperature stability.
Preferably, the compositions according to the invention comprise 100 parts by weight of vinylidene fluoride homopolymer, 2.1 parts by weight of B and 3.2 parts by weight of C, the homopolymer being chosen so as to have an MFI measured at 230° C., of 0.7 and a critical modulus G
C
, measured at 190° C., of 20 kPa.
Advantageously; with regard to the latter compositions, B is an acrylic elastomer and C is dibutyl sebacate.
The elastomers B which can be used in the context of the invention may be chosen from true elastomers and thermoplastic elastomers (TPEs). True elastomers or rubbers, whether natural or synthetic, are defined by the ASTM, Special Technical Bulletin No. 184 standard as materials capable of being drawn, at room temperature, up to twice their natural length and which, once released after being held under tension for 5 minutes, recover, to within 10, their initial length in the same time. TPEs have a
Pascal Thierry
Schlund Bruno
Elf Atochem S.A.
Mulcahy Peter D.
Smith , Gambrell & Russell, LLP
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