FR2684106A1 - Stabilised polyolefin composition - Google Patents

Abstract

This composition contains a metal thiosulphate. It can be used for the manufacture of moulded articles, extruded articles, pipes, films, foils, fibres, laminates and fibre coatings.

Description

STABILIZED POLYOLEFIN COMPOSITION
BACKGROUND OF THE INVENTION
Field of the invention
The subject of the present invention is a stabilized polyolefin composition containing minor amounts of a metal thiosulfate and optionally of a stabilizer other than a metal thiosulfate.

Description of the Related Prior Art
Specific compositions of polymers containing 0.1 to 5.0 parts of metal thiosulfate per 100 parts of copolymer are known. In these descriptions, metal thiosulfates are used in combination with other stabilizers.

 A particularly interesting reference is US Pat. No. 3,535,249 which describes a stabilization system for polymers comprising a phenolic antioxidant, a neutralizer based on heavy metal ions and a reducing agent. It is a composition of stabilized polymer further comprising an antioxidant to increase resistance to discoloration and to oxidation. The polymer compositions described are based on natural rubber, polybutadiene, butadiene rubber / styrene (SBR) and latex of the ABR type. and polymer derived therefrom.The composition contains from 0.03 to 5 parts at least of a phenolic antioxidant, from 0.25 to 5 parts of at least one neutralizer which makes it possible to neutralize the effect of metal ions heavy and from 0.25 to 5 parts of a component which may include a metal thiosulfate.

 US Patent No. 3,753,939 describes the stabilization of acrylamide polymers using thiosulfates. This patent describes compositions which include water-soluble acrylamide polymers and at least 0.1% by weight per relative to the weight of the soluble thiosulfate polymer It is indicated that the presence of the thiosulfate improves the stability to heat and to degradation by oxidation.

 U.S. Patent No. 4,041,015 describes metallic viscosity stabilizers for vinyl chloride polymers.

It is reported that the melt viscosity of vinyl chloride polymers is stabilized by linear polysulfides containing specific elements or organic radicals as end groups on the chains of sulfur atoms.

 US Patent No. 4,268,429 describes the use of a series of sulfur derivatives, including metal thiosulfates, in flame retardant polycarbonate compositions, used in an amount of not less than 0.5 parts per 100 parts of polycarbonate .

 US Pat. No. 4,581,405 describes the stabilization of dilute high molecular weight aqueous solution of homopolymers and copolymers based on water-soluble ethylenically unsaturated derivatives. It is stated that these derivatives are stabilized with respect to degradation by heat by adding at least 20 parts per million of organic sulfur derivative in which the sulfur has an oxidation index of +2 to +5, and at least 20 parts per million of a complexing agent metal ions This patent includes the use of 100 parts per million sodium thiosulfate as part of a stabilization composition for a sodium acrylate homopolymer.

 US Patent No. 4,598,119 describes stabilized emulsions of water-in-oil polyacrylate. The stability of an aqueous acrylate polymer such as sodium polyacrylate in dispersed aqueous phase of a water-in-oil emulsion is improved by the addition to the emulsion of a thiosulfate, of thiourea or of thiocyanate, soluble in water in an amount sufficient to improve the conservation of the viscosity of the polymer in aqueous solution. The stabilizing derivatives, including thiosulfates, are added in an amount of at least 0.5 * relative to the weight of the solution.

 US Patent No. 4,863,989 describes a water-absorbent resin composition. In the water-absorbent resin, a reducing mineral salt containing oxygen has been incorporated to improve the stability of the gel obtained. Specific examples of these salts include the metal thiosulfates, the salt being present in an amount of 0.001 to 10 parts by weight relative to the weight of the water-absorbent resin.

 U.S. Patent No. 4,537,922 describes compositions of sulfur stabilized oxidized polyolefins.

 It is known that hindered phenols are useful for stabilizing polymers, including polypropylene, as reported in U.S. Patent No. 3,285,855.

SUMMARY OF THIS INVENTION
The present invention relates to a polyolefin composition which comprises minor amounts of a metal thiosulfate. The use of minor amounts, preferably from S to 1500 parts per million, of a metal thiosulfate, preferably sodium thiosulfate or magnesium thiosulfate, has been found to confer stabilization on these polyolefins. This improved stability can be imparted to polyethylene, polypropylene homopolymers, or copolymers of ethylene and propylene. The improved stability has been observed in polymers not containing other functional groups such as double bonds or other reactive groups. Useful polyolefins include saturated homopolymers and copolymers.

 An improved stabilized polyolefin composition according to the present invention is the combination of minor amounts of metal thiosulfate and from 0.01 to 5.0 parts by weight of conventional stabilizers per 100 parts of polymer. Preferably, the conventional stabilizer is chosen from the group consisting of hindered phenolic derivatives, thioester derivatives and metal salts of carboxylic acids, preferably metal salts of group II monocarboxylic acid containing from 6 to 24 carbon atoms. Replacing a portion of a conventional stabilizer with an equal or lesser amount of the metal thiosulfate leads to the same or improved melt stability, as measured by the deterioration in flow properties at the molten state when repeated extrusions are carried out.

 For the purposes of the present invention, the term "ppm" means parts per million by weight relative to the polymer present. The term "pph" means parts per 100 by weight relative to the polymer present. The term "metal thiosulfate includes hydrated metal thiosulfates.

In consideration of these terms, the amount of hydrated metallic thiosulfate is based on the metallic thiosulfate present excluding the associated water.

BRIEF DESCRIPTION OF THE DRAWINGS
- Figure 1 gives curves of the flow index
in the molten state as a function of the number of
extrusions for examples 1 to 4 and
comparative example A;
- Figure 2 gives curves of the flow index
in the molten state as a function of the number of
extrusions for example 5 and examples
comparative B and C;
- Figure 3 gives curves of the flow index
in the molten state as a function of the number of
extrusions for example 6 and example
comparative D;
- Figure 4 gives curves of the flow index
in the molten state as a function of the number of
extrusions for examples 7 and 8 and
comparative example E;
- Figure 5 gives curves of the flow index
in the molten state as a function of the number of
extrusions for example 9 and examples
comparative ples F and G; ;
- Figure 5 gives curves of the flow index
in the molten state as a function of the number of
extrusions for examples 10 and 11 and
comparative example H.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF
THE INVENTION
The subject of the present invention is a stabilized polyolefin composition. The composition comprises minor amounts of a metal thiosulfate. The composition can optionally comprise at least one additional stabilizer other than a metal thiosulfate. It has been observed that the association of metal thiosulfate. with the additional stabilizer was more effective than an equivalent amount of the additional stabilizer alone.

 For the purposes of the present invention, "stability" was measured by the change in melt flow index measured in accordance with ASTM D-1238 during the extrusion of the composition, while first on a 46 mm diameter single screw Buss extruder, length / diameter ratio (L / D) equal to 7, at 230 "C, which is followed by consecutive repetitive extrusions through a Thoret extruder twin screw, at temperatures of about 250 to 270 "C. The screw diameter of the Thoret extruder is 25 mm and its L / D ratio is 9.2. The melt flow index according to standard ASTM D-1238 is measured at 230 "C, under 2.7 kg of pressure and the results are given in number of grams per 10 minutes.

 An increase in the value of the melt flow index indicates a reduction in stability which is believed to be due to a decrease in molecular weight by heat degradation. Degradation is believed to be due to cleavage by free radicals. Optionally, a decrease in stability can lead to color variations caused by possible side reactions.

 The composition according to the present invention comprises a polyolefin whose melt index can reach up to 100, and is preferably between 0.1 and 100, and preferably in particular between 0.1 and 60 and more particularly 0.2 and 15. The preferred polyolefins are polyethylene, polypropylene and copolymers of ethylene and propylene. The polyolefin homopolymer or copolymer of ethylene and propylene may contain up to 10 and preferably less than 3% of an additional comonomer.

It has been observed that improved stability is achieved according to the present invention when the polyolefin is substantially saturated and / or does not substantially contain other reactive or functional groups.

 Useful polyethylenes include the homopolymer or copolymers of ethylene which may be low density polyethylene, low density linear polyethylene or high density polyethylene. Typically, the specific gravity is between 0.9 and 0.965. The ethylene homopolymer can have a melt flow index of up to 100, preferably between 0.1 and 100, and more preferably 0.2 and 10. In polyethylene, the comonomer may be in a ratio of 0.01 to 1.0 with respect to ethylene and the range of melt flow index may be the same as that of homopolymers. Usually, low density polyethylene is manufactured at high pressures of 15,000 to 45,000 psi, using free radicals such as hydrogen peroxide or azo derivatives as catalysts. The specific density of low density polyethylene is between about 0.910 and about 0.935.

 Linear low density polyethylene, also known as low pressure polyethylene, is manufactured at low pressures, either by a solution process or by a gas phase process, using coordination catalysts such as a catalyst. Ziegler. Linear low density polyethylene contains branched chains significantly shorter than those of low density polyethylene. The specific density of linear low density polyethylene is between about 0.915 and about 0.935.

 High density polyethylene can be manufactured at temperatures of 60 to 80 "C and pressures below 1500 psig, as low as 100 psig, using an extremely active catalyst. Usually, the catalyst is an alkyl metal derivative , such as triethylene aluminum activated by titanium tetrachloride or another heavy metal derivative.

 Polypropylene usually includes the polypropylenes reviewed in Modern Plastics Encyclopedia, 1979-1980, published by McGraw Hill, Inc., New-York, New York, page 82. Polypropylene can be a propylene homopolymer whose index d flow in the molten state reaches up to 100 and is preferably between 1 and 100, and preferably in particular 1 and 40. Polypropylene can also include propylene copolymers in which the weight ratio of the comonomer to propylene is between 0.01 and 1 and preferably 0.05 and 0.5. The melt flow index of these copolymers reaches up to 100 and it is preferably between 1 and 100, and preferably in particular I and 50. Polypropylene can be produced by polymerization of propylene gas at high purity in low pressure reactors using heterogeneous catalysts of the Ziegler catalyst type. It is a crystalline polymer and its density is approximately equal to 0.90 g / cm.

Polypropylene is a thermoplastic material which can be extruded and shaped by methods used with other known thermoplastic compositions.

 Useful copolymers of ethylene and propylene may contain from 1 to 99% ethylene and a corresponding amount of propylene. The copolymer can also contain minor amounts, preferably up to 10%, and preferably in particular 0.1 to 5% of alpha-olefin containing 4 to 10 carbon atoms as termonomers. The ethylene / propylene copolymers include ethylene / propylene rubbers whose Mooney viscosity (ML1 + 4,125 "C) is between 10 and 80 and preferably 25 and 60. The weight ratio of ethylene to propylene is , preferably between 0.01 and 100 and preferably 0.5 and 40. Also useful are ethylene, propylene and diene monomers (EPDM terpolymers).

 The molecular weight of the polyolefins useful in the present invention can be any suitable molecular weight, from those of low molecular weight waxes having an average molecular weight as low as 1500, to those of polymers of extremely high molecular weight reaching up to 10,000,000; the typical molecular weight range being between 5,000 and 1,000,000 for more conventional polymers. The stabilizer according to the invention can stabilize polymers in the form of waxes, plastics, fibers and rubbers.

 The composition according to the present invention comprises the polyolefin described above and minor amounts of about 5 to 1,500 parts per million of a metal thiosulfate. For the purposes of the present invention, metal thiosulfates include hydrated metal thiosulfates. Relative amounts are based on the metal thiosulfate portion of the hydrated metal thiosulfate derivatives minus the amount of water. It is desirable to keep the metal thiosulfate at low levels to avoid discoloration of the composition.

The preferred metal thiosulfates correspond to the formula: M + j (S203 2 in which:
M is chosen from the metals of groups IA, IIA, IIB,
IIIA, IVA and VA of the Periodic Table of Elements;
j, k and h are positive integers between 1
and 4, provided that jxk = 2h.

 Preferred thiosulfate metal cations include lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, cadmium, aluminum, germanium, tin (+2 and +4), lead (+2 and +3) , sodium and magnesium being those which are particularly preferred.

 The composition contains from 5 to 1,500, preferably 10 to 1,250, preferably especially 20 to 1,100, more preferably 20 to 750 and more preferably especially 20 to 500 parts per million of metal thiosulfate relative to the polymer.

 According to yet another embodiment of the present invention, the composition may further comprise additional stabilizers useful for stabilizing the polyolefin derivatives. It has been observed that equivalent or lower amounts of other stabilizers, including sterically hindered phenolic derivatives, thioesters and metal carboxylic acid salts can be replaced by metal thiosulfate and equivalent stability is achieved. or improved. The preferred amounts of additional stabilizers are between 0.01 and 5, and preferably in particular 0.1 and 3 parts per 100 of polymer.

 The preferred stabilizers are selected from the group consisting of a product of a transesterification reaction of a polyvalent organic phenol and organic phosphite, the ester of an acid (4-hydroxy-5-alkylphenyl) alca noic and a metal salt of a monocarboxylic acid containing 6 to 24 carbon atoms and a metal from group II of the Periodic Table of the Elements.

dans laquelle:
X est choisi dans le groupe constitué par oxygène, sou
fre, radicaux alkylène, alicyclidène, arylidène et
alkylène-arylidène mixte et alkylène-alicyclidène mixte
dans lequel la portion aliphatique ou cycloaliphatique
de la molécule peut être une chaîne droite ou une
chaîne ramifiée renfermant de 1 à environ 18 atomes de
carbone;
les substituants R qui peuvent être identiques ou diffe-
rents, sont indépendamment choisis dans le groupe cons
titué par des atomes d'hydrogène et des radicaux alky
les à chaîne droite ou ramifiée;
m et n sont des nombres entiers compris entre 1 et 5;; et
o et p sont des nombres entiers compris entre 0 et 4, sous
réserve que les sommes m + o et n + p ne puissent pas
dépasser 5.The polyvalent organic phenols used to obtain the transesterification reaction product used in the polymer compositions according to the present invention correspond to the formula:

in which:
X is chosen from the group consisting of oxygen, sou
fre, alkylene, alicyclidene, arylidene and
mixed alkylene-arylidene and mixed alkylene-alicyclidene
in which the aliphatic or cycloaliphatic portion
of the molecule can be a straight chain or a
branched chain containing from 1 to about 18 atoms of
carbon;
the substituents R which can be identical or different
rents, are independently selected from the cons group
titled by hydrogen atoms and alkyl radicals
straight or branched chains;
m and n are whole numbers between 1 and 5 ;; and
o and p are whole numbers between 0 and 4, under
provided that the sums m + o and n + p cannot
exceed 5.

The OH groups are preferably in the ortho and / or para position with respect to X.

The products of a transesterification reaction of organic polyvalent phenols and organic phosphite triesters suitable for use in the presently claimed invention are, for example, described in US Pat. Nos. 3,244,650 and 3,255,136, both on behalf of
Hecker et al. The description of these transesterification products given here is mainly based on that given in US Patent No. 3,244,650 to Hecker et al,
As described in US Patent No. 3,244,650, suitable polyvalent phenols include orcinol, catechol, resorcinol, p-octylresorcinol, p-docecylresorcinol, p-octadecylcatechol, p-isooctyl-phloroglucinol, pyrogallol, hexahydroxybenzene, p-isohex 6-ditertiobutyl resorcinol, 2,6-diisopropylphloroglycinol, methylenebis (2,6-ditertiobutyl-m-cresol), methylenebis- (2, 6-ditertiobutylphenol), 2,2-bis (4-hydroxyphenyl) propane, methylene bis (cresol), 4,4 '-thio-bis (3-methyl-6-tertiobutylphenol), 2,2' -oxobis (4-dodecylphenol), 2,2'-thio-bis (3-methyl-6tertiobutylphenol), 2,2-thio-bis (4-methyl-6-tertiobutylphenol), 2,6-diisooctyl-resorcinol, 4,4 '-n-butylidene-bis- (2,4-butyl-5-methylphenol), 4, 4'-benzylidene-bis (2-t-butyl-5-methylphenol), 2,2 '-methylene-bis (4-methyl-6-l' -methyl- cyclohexylphenol), 4,4 '-cyclohexylidene-bis ( 2-t-butylphenol), 2,6-bis (2'-hydroxy-3-t-butyl-5'-butylbenzyl) -4-methylphenol, 4-octyl-plyrogallol and 3, 5 -ditertiobutylcatéchol.

 The polyvalent phenols which are particularly preferred are 4,4 '-n-butylidene-bis (6-tert-butyl-m-cresol) and 1,1,3 tris (2-methyl-4-hydroxy-5 -tert-butylphenyl) butane.

 The organic phosphites suitable for the preparation of the transesterification reaction products of organic polyvalent phenol and of organic phosphite triester used in the stabilizer compositions according to the present invention are also described in the U.S. patent.

 No. 3,244,650. It can be any organic phosphite corresponding to the formula (Ra) 3P, in which a is chosen from the group consisting of oxygen, sulfur and their mixtures, and R is chosen from the grouped by aryl, alkyl, cycloalkyl, arylalkyl, alkylaryl radicals and combinations thereof The term "organic phosphite triester" as used herein includes oxo, thio and mixed oxo-thio phosphites. For reasons of availability, usually the phosphite cannot contain more than 60 carbon atoms.

Suitable phosphites include, by way of example, those listed in US Pat. No. 3,244,540, that is to say:
- monophenyl-di-2-ethyl-hexylphosphite,
- diphenyl-mono-2-ethylhexylphosphite,
- diisooctyl-monotolylphosphite,
- tri-2-ethylhexylphosphite,
- phenyldicyclohexylphosphite,
- phenyldiethylphosphite,
- triphenylphosphite,
- tricresylphosphite,
- tri (dimethylphenyl) phosphite,
- trioctadecylphosphite,
- triisooctylphosphite,
- tridodecylphosphite,
- isooctyldiphenylphosphite,
- diisooctylphenylphosphite,
- tri (t-octylphenyl) phosphite,
- tri (t-nonylphenyl) phosphite,
- benzylmethylisopropylphosphite,
- butyldicrésylphosphite,
- isooctyldi (octylphenyl) phosphite,
- di (2-ethylhexyl) (isooctylphenyl) phosphite,
- tri (2-cyclohexylphenyl) phosphite,
- tri-alpha-naphthylphosphite,
- tri (phenylphenyl) phosphite,
- tri (2-phenylethyl) phosphite,
- tridodecylthiophosphite,
- tri-p-tert-butylphenylthiophosphite,
- dodecylthiodiphenylphosphite, and
- tert-butylphenylthio-di-2-ethylhexylphosphite.

 The transesterification product can constitute from 0.1 to 3.0%, and preferably from 0.1 to 0.5%, by weight relative to the weight of the polymer. The most preferred transesterification product is 4,4-n butylidene-bis (6-tert-butyl-m-cresol) phosphite.

 Transesterification reaction products of organic polyvalent phenols and organic phosphite triesters free of hydroxylphenolic groups can be obtained by heating the phenol and the phosphite ester together, preferably at temperatures from 100 to 2009C and, if necessary , at reflux. To accelerate transesterification, it is preferable to add a small amount of alkali or alkaline earth metal oxide, hydroxide or phenolate in an amount of about 0.05 to about 1% by weight. Usually, a transesterification involving about 1/3 of the phosphite ester groups of the triphosphite and about half of the available phenolic groups of the divalent phenol, on a mole-to-mole basis, may be sufficient.

dans laquelle:
les substituants R qui peuvent etre identiques ou diffe
rents, sont indépendamment choisis dans le groupe cons
titubé par un atome d'hydrogène et un radical alkyle à
chaîne droite ou ramifiee renfermant d'environ 1 à
environ 18 atomes de carbone;
m et n étant des nombres entiers de O à 2; et
o et p étant des nombres entiers de 1 à 5, sous reserve que
les sommes m + o et n + p ne puissent pas dépasser 5.The sterically hindered phenols preferably comprise a pentaerythritol diphosphite corresponding to the general formula:

in which:
the substituents R which can be identical or different
rents, are independently selected from the cons group
titubated by a hydrogen atom and an alkyl radical with
straight or branched chain containing from about 1 to
about 18 carbon atoms;
m and n being whole numbers from O to 2; and
o and p being whole numbers from 1 to 5, provided that
the sums m + o and n + p cannot exceed 5.

The stabilizer constitutes from 0.2 to 3.0 and preferably from 0.2 to 0.8% by weight relative to the weight of the polymer. The preferred stabilizer is bis (2,4-di-t-butylphenyl] - penta8rythritol-diphosphite corresponding to the formula:

 This product is sold by Borg-Warner Chemical, Inc.

under the name of Ultranox TM 624 and it is described in the bulletin Ultranox TM Anti-oxidant, Technical Literature, CA243A, 8305 AM.

dans laquelle:
R1 représente un radical méthyle, éthyle ou alkyle alpha
ramifié renfermant de 3 à 10 atomes de carbone;
R2 est un atome d'hydrogène, un radical méthyle, éthyle ou
alkyle alpha-ramifié renfermant de 3 à 10 atomes de
carbone;
v a une valeur de 1 à 6;
w a une valeur de 2 à 6;
z est un hydrocarbure aliphatique répondant à la formule:
CH
y 2y+2-w
dans laquelle y a une valeur de 2 à 18 lorsque w a une
valeur de 2 et une valeur de 3 à 6 lorsque n est supé
rieur à 2, la valeur de y dans tous les cas étant égale
ou supérieure à celle de w.A preferred stabilizer system includes the ester of a (4-hydroxy-5-alkylphenyl) alkanoic acid. The ester meets the formula:

in which:
R1 represents a methyl, ethyl or alpha alkyl radical
branched containing 3 to 10 carbon atoms;
R2 is a hydrogen atom, a methyl, ethyl or
alpha-branched alkyl containing 3 to 10 atoms of
carbon;
goes from 1 to 6;
wa has a value from 2 to 6;
z is an aliphatic hydrocarbon corresponding to the formula:
CH
y 2y + 2-w
where there is a value from 2 to 18 when wa a
value of 2 and a value of 3 to 6 when n is greater
laughing at 2, the value of y in all cases being equal
or greater than that of w.

 An alkyl group (R1) is preferably located ortho to the hydroxy group. A second identical or different alkyl group (R2) is also present either (a) in the other position ortho with respect to the hydroxy group and (position 3) or (b) meta with respect to the hydroxy group and para with respect to the first alkyl group (position 2).

These alkyl groups can be a methyl or ethyl radical or, when they are greater than the ethyl radical, an a-branched alkyl radical containing from 3 to 10 carbon atoms. The term "a-branched alkyl radical" means a radical in which the carbon atom of the alkyl radical which is linked to the phenyl group is also linked to at least two other carbon atoms of the alkyl group.

 Thus, the mono- or dialkylphenolic group comprises for example 3,5-di-tertiobutyl-4-hydroxyphenyl, 3,5-dimethyl- 4-hydroxyphenyl, 3,5-diisopropyl-4-hydroxyphenyl, 2,5-dimethyl-4 -hydroxyphenyl, 2-methyl-4-hydroxy-5-tertiobutylphenyl, 2-methyl-4-hydroxy-5-isopropylphenyl, 3-methyl-4 hydroxy-5-tertiobutylphenyl, 3, 5-diethyl-4-hydroxyphenyl and the like. The preferred phenolic groups are those containing at least one branched group such as for example isopropyl, tert-butyl or the like in a position ortho with respect to the hydroxy group.

 The mono- or dialkyl-4-hydroxyphenyl group is linked to an alkanoyl unit containing from 2 to 7 carbon atoms. The hydrocarbon portion of this alkanoyl unit is represented by - (CVH2v) - and can be a straight chain or, when v is greater than I, a branched chain. One of the preferred alkanoyl groups is the 3-propionyl group.

Two or more than two (as determined by an integer w) of these mono- or dialkylphenylalkanoyl groups are then linked by an equal number of carbon atoms to the hydrocarbon residue of a polyol. The polyol from which these esters are derived can thus consist of the straight chain or branched chain hydrocarbon residue corresponding to the formula
CyH2y + 2 w and a number of hydroxy groups equal to w. When w is equal to 2, that is to say that the polyol is a diol, this hydrocarbon residue can contain from 2 to 12 carbon atoms. When w is greater than 2, i.e. the polyol is a triol, tetrol, pentol or hexol, the residual hydrocarbon can contain from 3 to 6 carbon atoms. In all cases, the number of groups hydroxy and the resulting number of alkylphenylalkanoyloxy groups (as denoted by w) will be equal to or less than the number of carbon atoms (y) in the hydrocarbon residue; that is, since each carbon atom in the hydrocarbon residue can carry only one hydroxy group, y is equal to or greater than w.

dans laquelle:
chacun d'entre R1 et R2 représente un radical méthyle,
éthyle ou un radical alkyle alpha-ramifié renfermant de
3 à 6 atomes de carbone, de préférence, R1 et R2 repré
sentent chacun le radical tertiobutyle.Representatives of the esters which can be used in the stabilizing system of the composition according to the present invention include, but are not limited to, the following esters described in US Patent No. 3,644,482, esters characterized by the formula:

in which:
each of R1 and R2 represents a methyl radical,
ethyl or an alpha-branched alkyl radical containing
3 to 6 carbon atoms, preferably R1 and R2 represented
each feel the tert-butyl radical.

 Preferably in particular, the ester is a diester of 3- (3,5-di-tert-butyl-4-hydroxyphér.yl) propionic acid of a diol.

Diols can include: ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentylglycol, 1,6-hexanediol, 2-methyl-1,4-pentanediol, 2,2,4 -tri methyl-1,3-pentanediol, 2,4-dimethyl-2,4-pentanediol, 2,4,4 trimethyl-1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10 -decanediol, 1,2-dodecanediol, 1,12-octadecanediol and 1,18-octadecanediol. The esters which are specifically preferred include: ethylene glycol bis- (3- (3,5 -di-tertiobutyl- 4-hydroxyphenyl) propionate3, 1, 2-propylene glycol-bis- (3- (3,5-di-tertiobutyl-4-hydroxyphenyl) propionate], neo-pentyl-glycol-bis- (3- (3,5-di-tertiobutyl-4 -hydroxyphenylpropionate], 1,6-hexanediol-bis- [3- (3,5-di-tertiobutyl-4-hydroxyphenyl) propionate], and 1,9-nonanediol-bis- (3- (3,5- di-tertiobutyl-4-hydroxyphenyl) propionate].

The esters which can be used in the stabilizing system according to the present invention include esters in which Z of formula IV corresponds to the formula:
CyH2y + 2-W 'y having a value of 3 to 6, and the value of y being equal to or greater than the value of w. Preferably, - R1 and R2 of formula IV each represent the tert-butyl radical. Preferably, the esters comprise: pentaerythritol-tetrakis- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) - propionate], 1,1,1-trimethylol-ethane-tris- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 1,1,1-trimethylol-propane- tris- (3- (3 , 5-di-tertiobutyl-4-hydroxyphenyl) propionate], glycerin-tris- (3- (3,5-di-tertiobutyl-4-hydroxyphenyl) propionate] and sorbitol-hexakis- (3- (3,5 -di-tertiobutyl-4-hydroxyphenyl) propionate].

 Other esters which can be used in the stabilizing system according to the present invention also include pentaerythritol-tetrakis- (3- (3-methyl-4-hydroxy-5-tert-butylphenyl) propionate] and pentaerythritol-tetrakis- (3 (3,5-dimethyl-4-hydroxyphenyl) propionate].

 The composition according to the present invention may comprise from 0.1 to 3.0%, and preferably 0.1 to 0.5% by weight of ester relative to the weight of the polymer. One of the preferred esters is tetrakisCmethylene-3- (3 ', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate].

dans laquelle
x est égal à 2 à 6, et
y est égal à 2 à 10, de préférence utilisé sous la forme d'Irganox 1098 répondant à la formule:

dans laquelle:
x est égal à 2 à 6, et
y est égal à 2 à 10, utilisé de préférence sous la forme de Goodrite 3125 présentant la formule::

Other sterically hindered phenolic derivatives useful in the present invention are: 2,6-di-tertiobutylphenol, 2,6-di-tertiobutyl-p-cresol, 2,4-dimethyl-6-tertio butylphenol, butylhydroxyanisole, 1, 1-bis- (4-hydroxyphenyl) - cyclohexane, 2,2'-methylenebis- (4-methyl-6-tertiobutylphenol), 2,2'-methylenebis- (4-ethyl-6-tertiobutylphenol), 4, 4'-butylidenebis- (3-methyl-6-tertiobutylphenol), 4,4'-thiobis- (3-methyl-6-tertiobutylphenol), 1,1,3-tris- (2-methyl-4-hydroxy-5 -tertiobutylphenyl) butane,

in which
x is 2 to 6, and
y is equal to 2 to 10, preferably used in the form of Irganox 1098 corresponding to the formula:

in which:
x is 2 to 6, and
y is equal to 2 to 10, preferably used in the form of Goodrite 3125 having the formula:

 The thioesters useful as stabilizers in the present invention correspond to the formula: (ROOC-CH2CH2) nS, R being an organic derivative, preferably an aliphatic derivative containing from 1 to 18 carbon atoms, and n being equal to 1 to 6, and preferably 2 to 4.

 Other useful stabilizers include a salt of a monocarboxylic acid containing from about 6 to 24 carbon atoms and a metal from group II of the Periodic Table of the Elements. The metal can, for example, be any of zinc, calcium, cadmium, barium, magnesium and strontium. The acid can be any organic monocarboxylic acid containing about 6 to 24 carbon atoms and which does not contain nitrogen. Suitable acids are also described in U.S. Patent No. 3,244,650.

As noted in this reference, the aliphatic, aromatic, alicyclic and heterocyclic organic acids containing oxygen are functional as a class. The term "aliphatic acid" includes any open chain carboxylic acid unsubstituted or substituted by non-reactive groups, such as, for example, halogen, sulfur or hydroxyl atoms. The term "alicyclic acid" includes any carboxylic acid containing a non-aromatic ring, optionally substituted with a non-reactive substituent, such as halogen atoms, hydroxyl groups or alkyl and alkenyl radicals, or the like. Cyclic carboxylic structures. Suitable aromatic acids can be oxygen-containing carboxylic or heterocyclic and can be substituted with a non-reactive ring substituent such as halogen, alkyl or alkenyl radicals and other saturated or aromatic rings condensed therewith. For example, suitable acids include those listed in US Patent No. 3,244,650, for example hexoic acid, 2-ethylhexoic acid, n-octoic acid, isooctoic acid , caproic acid, undecylic acid, lauric acid, myristic acid, palmitic acid, inorgaric acid, stearic acid, oleic acid, ricinoleic acid, acid behenic, chlorocaproic acid, hydroxycaproic acid, benzoic acid, phenylacetic acid, butylbenzoic acid, ethylbenzoic acid, propylbenzoic acid, hexylbenzoic acid, salicylic acid, naphthoic acid, 1-naphthalene-acetic acid, orthobenzolyl-benzoic acid, naphthic acids abietic acid, dihydroabietic acid, hexanhydrobenzoic acid and methylfuroic acid.

Other stabilizers that can be used with thiosulfate include:
H37C18S (C-hexyl) hexyl) (CH2) 2SC18H37, and
BuSn (S) SC12H25.

 The composition according to the present invention may also contain one or more additives, lubricants and release agents, colorants, including dye and pigments, flame retardants, fibrous and particulate fillers and reinforcing agents, nucleators, plasticizers, and other classics. These additives are commonly added during the mixing step.

 The compositions according to the invention can be prepared by melt-blending the polyolefin composition to form a uniform mixture in a screw extruder, or any other conventional plasticizing device such as a Brabender, a Banbury mixer, a grinder, etc. The composition is mixed in the molten state at a temperature above the melting temperature of the polyolefin. Preferably, the composition is mixed in the molten state at a temperature of at least 6 "C higher than the melting temperature of the polymer and lower than the temperature at which significant degradation occurs. Preferably, the composition is prepared by melt mixing at a temperature of 6 to 42 "C (10 to 75" F), and preferably 6 to 17 "C (10 to 30" F), higher than the melting temperature of the polyolefin having the highest melting temperature in the composition.

 The compositions can be transformed into a whole series of useful articles, by conventional molding methods used in the manufacture of thermoplastic articles, i.e. molded parts, extruded forms, tubes, films, sheets, fibers, laminates. and film coatings.

The term "molding" means the shaping of an article by deformation of the mixture in the hot plastic state.

 The following examples illustrate the practice of the present invention. The examples should not be interpreted as limiting the invention to a lesser scope than what is described or which would have been obvious to a specialist of ordinary skill in this technique. Percentages and parts are given by weight, unless otherwise indicated.

- IrgafosX 168 fabriqué par Ciba-Geigy Corp. et présen
tant la formule:

- Goodrite 3114 fabriqué par B.F. Goodrich Corp. et
presentant la formule:

- Ethanox 330 fabriqué par Ethyl Corp. et présentant la
formule:

The stabilizers used in the examples will be indicated below:
- Irganox 1010 manufactured by Ciba-Geigy Corp. and present
both the formula:

- IrgafosX 168 manufactured by Ciba-Geigy Corp. and present
both the formula:

- Goodrite 3114 manufactured by BF Goodrich Corp. and
presenting the formula:

- Ethanox 330 manufactured by Ethyl Corp. and presenting the
formula:

 All the examples below are carried out in accordance with the following operating mode. A homogeneous mixture of polyolefin and stabilizing derivatives is prepared in the form of a powder. The mixture is mixed in the molten state on a Buss twin-screw 23cor extruder. Each melted mixed sample is then extruded five consecutive times through a twin-screw Thoret extruder at a temperature of about 250 to 270 "C. After each pass through the Thoret extruder, the flow index is measured in the molten state.

 The melt flow index (MFI) is tested in accordance with standard ASTM D-1238 at 230 "C under 2.16 kg of pressure, the results being given in grams per 10 minutes (g / 10 min ).

 The Mooney viscosity is measured according to the French standard NFT 43 005 (corresponding to the standard ASTM D-1656). The torque is measured using a flat rotor in contact with the material. The Mooney viscosity is indicated as ML t1, t2 at 125 "C, M meaning Mooney, L meaning a large rotor, t1 the preheating time and t2 the time spent at 125" C.

EXAMPLES 1 to 4
The compositions of Examples 1 to 4 contain a block copolymer of propylene and ethylene sold by Appryl.

The weight ratio of propylene to ethylene is 9.

The melt flow index (MFI) of this polymer is equal to 6 before extrusion. The compositions contain 500 parts per million of calcium stearate and 500 parts per million of hydrotalcite (Mg6AI2COH) 16C03.4H20], and hydrated thiosulfate corresponding to the formula Na2S203.5H20 in Examples 1 to 4 at respective levels of 500 , 750, 1,000 and 1,250 parts per million (ppm). The composition of Comparative Example A does not contain sodium thiosulfate. The results are given in FIG. 1. Examination of FIG. 1 reveals that, when the level of sodium thiosulfate increases, the stability decreases. However, even for 500 parts per million, there is a significant improvement in stability.

EXAMPLE 5
In this composition, the amounts of polymer, calcium stearate and hydrotalcite are the same as in Examples 1 to 4. In Example 5, 320 ppm of sodium thiosulfate corresponding to the formula Na2S203 are also used. In Example 5, 500 parts per million of Irganox 1010 are used. In Comparative Example B, only 500 parts by weight of Irganox 1010 are used and in Comparative Example C, 500 parts of Irganox 1010 + 500 parts of Irgafos 168. The results are noted in FIG. 2. These results show that the addition of sodium thiosulfate leads to a significant improvement compared to the use of Irganox 1010 alone. Furthermore, Comparative Example C deals with a composition which is known to be useful in the prior art. Example 5 gives performances slightly better than those of the prior art system using a corresponding quantity more lower sodium thiosulfate than Irgafos 168.

EXAMPLES 6 TO 8
Examples 6 to 8 are based on a composition in which the amounts of polymer, calcium stearate and hydrotalcite are the same as in the inventive and comparative examples above. Examples 6 to 8 each used 250 parts per million of hydrated sodium thiosulfate of the same type as that used in Examples 1 to 4. In addition, Example 6 uses 500 parts per million.
Goodrite 3114. Example 7 uses 1000 parts of Ethanox 330 and in the example 800 parts of Ethanox 330. Comparative example D uses 500 parts of Goodrite 3114 and 500 parts of Irgafos 168 in the absence sodium thiosulfate.

Comparative Example E uses 1,000 parts of Ethanox 330 in the absence of an additional stabilizing agent.

 The results are given in Figures 3 and 4. Figure 3 shows the equivalence of 250 parts of hydrated thiosulfate (pentahydrate) instead of the more expensive Irgafos 168.

FIG. 4 also shows that, for a reduced level of thiophosphate, the present example leads to a much better performance than an equivalent amount of Ethanox 330. Reference will be made in particular to Example 8 and to Comparative Example C .

EXAMPLE 9
Example 9 is based on the same compositions containing the same polymer and the same levels of calcium stearate and hydrotalcite as in Example 1 to 4. Example 9 uses 500 parts of Irganox 1010 and 200 parts of thiosulfate magnesium hydrated by 6 molecules of water. Comparative example F uses only 500 parts of Irganox 1010 and comparative example G 500 parts per million of Irganox 1010 and 500 parts of Irgafos 168. Figure 5 shows the positive effect of magnesium thiosulfate. The addition of 250 parts of magnesium thiosulfate to the 500 parts per million of Irganox 1010 gives a higher performance than that of Irganox 1010 alone or in combination with Irgafos 168.

EXAMPLES 10-11
Examples 10 and 11 relate to a random polyethylene-propylene copolymer prepared by Solvay under the name KL 001 P in association with 1,000 parts per million of calcium stearate. In Example 10, the composition also comprises 666 parts of Irganox 1010 and 300 parts of magnesium thiosulfate of the type used in Example 9.

Example 11 relates to the same composition as that of Example 10 except that 500 parts of magnesium thiosulfate are used. Comparative example H uses 666 parts of Irganox 1010 and 1,337 parts per million of Irgafos 168.

The results are shown in FIG. 6. Again here, the use of magnesium thiosulfate (MgS203.6H2O) leads to an improvement in stability.

 Although embodiments of the present invention have been given by way of example, the true scope of the invention should be determined from the following claims.

Claims (22)

 1.- A composition comprising:  - a polyolefin, and  - from 5 to 1,500 ppm of metallic thiosulfate.  2. The composition according to claim 1, characterized in that the polyolefin is chosen from the group consisting of polyethylene, polypropylene and ethylene / propylene copolymers.  3. The composition according to claim 2, characterized in that the polyolefin is a copolymer of ethylene and propylene.  4. The composition according to claim 2, characterized in that the polyolefin is saturated.  5. The composition according to claim 1, characterized in that the metal thiosulfate corresponds to the formula: M + jt (S203) h in which:  M is chosen from the metals of groups IA, IXIA, IIB,  IIIA, IVA and VA of the Periodic Classification of  Elements;  j, k and h are positive integers between 1 and 4,  provided that j x k = 2h.  6.- The composition according to claim 5, characterized in that M is chosen from sodium and magnesium.  7.- The composition according to claim 1, characterized in that it contains from 10 to 1250 ppm of a metal thiosulfate.  8.- The composition according to claim 7, characterized in that it contains from 20 to 1000 ppm of a metal thiosulfate.  9. The composition according to claim 7, characterized in that it contains from 20 to 750 ppm of a metal thiosulfate.  xylic.  thioesters and a metal salt of a carbo acid  sterically hindered phenolic derivatives,  chosen from the group consisting of  - from 0.01 to 5.0 pph of at least one additional stabilizer  - from 5 to 1,500 ppm of a metal thiosulfate; and  - a polyolefin;  10.- A composition comprising:  11.- The composition according to claim 10, characterized in that the polyolefin is chosen from the group consisting of polyethylene, polypropylene and copolymers of ethylene and propylene.  12.- The composition according to claim 11, characterized in that the polyolefin is a copolymer of ethylene and propylene.  13.- The composition according to claim 11, characterized in that the polyolefin is saturated.  14.- The composition according to claim 10, characterized in that the metal thiosulfate corresponds to the formula:  k (S203) h in which:  M is chosen from the metals of groups IA, IIA, IIB,  IIIA, IVA and VA of the Periodic Classification of  Elements;  j, k and h are positive integers between 1 and 4,  provided that j x k = 2h.  15.- The composition according to claim 14, characterized in that M is chosen from sodium and magnesium.  16.- The composition according to claim 10, characterized in that the additional stabilizer is chosen from the group consisting of a transesterification reaction product of a polyvalent organic phenol and an organic phosphite, the ester of an acid (4-hydroxy-5-alkylphenyl) alca noic, a metal salt of a monocarboxylic acid containing 6 to 24 carbon atoms and a metal from group II of the Periodic Table of the Elements.  17.- The composition according to claim 10, characterized in that it contains from 10 to 1250 ppm of a metal thiosulfate.  18.- The composition according to claim 17, characterized in that it contains from 20 to 1000 ppm of a metal thiosulfate.  19.- The composition according to claim 18, characterized in that it contains from 20 to 750 ppm of a metal thiosulfate.  20.- An improved polyolefin composition of the type containing at least one stabilizer chosen from the group consisting of hindered phenolic derivatives, thioester derivatives and a metal salt of a carboxylic acid, characterized by the addition of 5 to 1,500 ppm of a metal thiosulfate.  21.- A composition comprises a substantially saturated polyolefin and from 5 to 1500 ppm of a metal thiosulfate.  22.- The composition according to claim 19, characterized in that the polyolefin is chosen from the group consisting of polyethylene, polypropylene and copolymers of ethylene and propylene and contains less than 3% by weight of additional comonomer.