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...
Reexamination Certificate
1999-06-10
2001-11-20
Mulcahy, Peter D. (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...
C524S396000, C524S397000, C524S399000
Reexamination Certificate
active
06319972
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions containing vinylidene fluoride polymers exhibiting an improved thermal stability.
It more particularly relates to such compositions containing a bismuth carboxylate as heat stabilizer.
Technology Review
Vinylidene fluoride polymers, which are thermoplastic homopolymers and copolymers, constitute well known polymers exhibiting an array of advantageous properties and, in particular, high chemical inertia and high resistance to ultraviolet radiation, as well as excellent mechanical strength. These polymers consequently know numerous applications in fields, such as for example in the chemical industry, which are particularly demanding as regards resistance to corrosion. In addition, these polymers exhibit an excellent intrinsic thermal stability, so that they are most often employed in the absence of any heat stabilizer.
Nevertheless, in applications in which these polymers are employed as a very thick layer, for example of the order of several tens of mm, thermal degradation can appear at the core of the material as a result of the severe thermal conditions to which it is subjected during the shaping of thick components. Likewise, problems of thermal stability emerge when vinylidene fluoride polymers of very high molecular weights are melt-shaped (for example for the shaping of articles requiring very high mechanical strength) and/or when vinylidene fluoride copolymers, the intrinsic thermal stability of which is less than that of the homopolymer, are melt-shaped. It thus proves to be currently desirable to have available heat stabilizers which are effective for vinylidene fluoride polymers.
A multitude of very diverse heat stabilizers have already been proposed for the (essential) thermal stabilization of chlorinated polymers, such as vinyl chloride polymers. In practice, they are most often salts of lead, calcium and/or zinc, barium and/or cadmium or alternatively organotins and thiotins.
Nevertheless, in Patent CH-A-275,161 of Apr. 20, 1948, a description is given of the thermal stabilization of vinyl chloride and vinylidene chloride polymers by the involvement of bismuth salts of highly varied organic acids, such as, for example, bismuth formate, maleate, laurate and stearate, preference being given to the bismuth salts of fatty acids having at least 12 carbon atoms.
The thermal stabilization of poly(vinyl chloride) polymers by the involvement of bismuth salts of C
6
to C
22
monocarboxylic acids, such as in particular bismuth stearate and salicylate, is recommended in Patent Application JP-A-66/19821 of Aug. 30, 1963. These bismuth salts are advantageously employed in conjunction with heat stabilizers, such as cadmium, barium, zinc or lead salts.
SUMMARY OF THE INVENTION
The present invention is targeted at providing heat stabilizers which are effective for vinylidene fluoride polymers.
To this end, the invention relates to compositions containing vinylidene fluoride polymers which are stabilized to heat by the involvement of an effective amount of bismuth carboxylate, characterized in that the bismuth carboxylate is chosen from bismuth succinate, acrylate and terephthalate and their mixtures.
Excellent results are obtained with the succinate and the acrylate and their mixtures. A very particularly preferred bismuth carboxylate is the succinate.
DETAILED DESCRIPTION OF THE INVENTION
A surprising aspect of the present invention is the fact that bismuth carboxylates described as being capable of contributing effectively to the thermal stabilization of chlorinated polymers, and which are moreover similar to the bismuth carboxylates employed in the compositions according to the invention, prove to be ineffective in stabilizing vinylidene fluoride polymers. Moreover, the effectiveness of the heat stabilizers according to the invention is such that they even make possible the stabilization/decoloration of thermally degraded waste vinylidene fluoride polymers.
Effective amount of bismuth carboxylate is understood to denote, for the purposes of the present invention, an amount which is sufficient to improve the thermal stability, that is to say to prevent the coloration of the compositions or, depending on the situation, to reduce the coloration of the compositions (in the case of the stabilization of waste polymers which are already degraded) when the latter are subjected to temperatures higher than the melting temperature of the vinylidene fluoride polymers and which are sufficient to be able to convert them into shaped articles. This amount is not particularly critical and depends, in particular, on the nature, on the molecular weight and, if appropriate, on the extent of the thermal degradation of the vinylidene fluoride polymers which it is desired to stabilize. To give an idea, the bismuth carboxylate is generally employed in the proportion of at least 0.05 part by weight, most often at least 0.1 part by weight and more particularly still at least 0.3 part by weight per 100 parts by weight of vinylidene fluoride polymer. In general, the bismuth carboxylate content does not exceed 5 parts by weight; most often it does not exceed 3 parts by weight and more particularly still 1.5 parts by weight per 100 parts by weight of vinylidene fluoride polymer.
The manufacture of the bismuth carboxylates employed in the compositions according to the invention does not have a critical nature. The carboxylates can therefore be manufactured in any appropriate way. It is possible, for example, to manufacture them by a wet route by reacting, in water at room temperature, stoichiometric amounts of bismuth hydroxide and carboxylic acid (succinic, acrylic or terephthalic acid or their mixtures), followed by filtration of the bismuth salt. It is also possible to manufacture them by a dry route, for example by dry mixing/grinding, for a few minutes, appropriate amounts of bismuth trioxide and the carboxylic acid (mechanochemical reactions), followed by reheating the reaction mixture to complete the reaction.
The bismuth carboxylate can be employed in any form, for example powder or aqueous dispersion. However, for reasons of convenience, it is preferable to employ it in the form of a powder. In this case, it is advantageous to use powders in which the particles exhibit a mean diameter of less than approximately 100 &mgr;m. The mean diameter of the bismuth carboxylate particles is preferably between approximately 0.1 and 30 &mgr;m.
In addition to the bismuth carboxylate, the compositions according to the invention can contain the usual additives for vinylidene fluoride polymers, such as lubricating agents, pigments, additives which reduce the emission of smoke during combustion (“smoke-suppressants”), and the like. In general, the compositions according to the invention do not contain a heat stabilizer other than the bismuth carboxylate.
Vinylidene fluoride polymer is understood to denote, for the purposes of the present invention, both vinylidene fluoride homopolymers and thermoplastic copolymers of vinylidene fluoride and of ethylenically unsaturated comonomers, which are advantageously fluorinated, containing at least approximately 75% by weight of monomer units derived from vinylidene fluoride The said thermoplastic copolymers advantageously exhibit a melting temperature at least equal to 130° C. and preferably at least equal to 150° C. and more particularly still 165° C. Mention may be made, as examples of fluorinated comonomers which can be used, of hexafluoropropylene and chlorotrifluoroethylene.
The vinylidene fluoride polymers of the compositions according to the invention are advantageously chosen from vinylidene fluoride homopolymers and its thermoplastic copolymers with hexafluoropropylene or chlorotrifluoroethylene, and more particularly with chlorotrifluoroethylene. The thermoplastic copolymers of vinylidene fluoride and of hexafluoropropylene advantageously contain from 5 to 20% by weight approximately of hexafluoropropylene and more particularly still from 8 to 15% by weight approximately. The latter particularly pr
Bromont Valerie
Hannecart Etienne
Robin Jean-Jacques
Mulcahy Peter D.
Schneller Marina V.
Solvay S.A.
Venable
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