GB1593902A - Stabilisation of polymers - Google Patents

Abstract

A stabiliser combination comprising a deactivator and an oxidation inhibitor for polymers in contact with copper is described. A stabiliser combination of this type contains unsubstituted N,N'-bis-salicyloylhydrazine as deactivator and oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline as oxidation inhibitor. This stabiliser combination is particularly suitable for polymers used as cable and wire insulation in high-voltage and communications technology. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO THE STABILISATION OF POLYMERS (71) We, SIEMENS AKTIENGESELLSCHAFT, a German Company, of Berlin and Munich, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a stabiliser combination for use with polymers which are in contact with copper, and to polymer compositions incorporating such a stabiliser combination.

Many organic polymers such as polyolefines and polyoxy-methylenes, which are used in the electrical industry for insulation purposes, have such physical and electrical properties, that they undergo accelerated ageing caused by thermo-oxidation when in the presence of copper; this ageing has an adverse effect on the electrical and mechanical properties of the polymers. Copper has a particularly serious influence on polymers at high temperatures, since the rate of ageing of the polymers increases considerably as temperatures rise. In order that polymers should possess the required quality and thermal loading capacity stabilisers are accordingly employed, in an attempt to guarantee that the polymers are sufficiently protected in the presence of copper, especially at high temperatures.

Particular difficulties arise when long-term stabilisation of insulations based on polyolefines is required for cables and conduits with copper conductors, which are to be subjected to a continuous operating temperature of at least 90"C. Crosslinked polyolefines are preferably used for such insulations. With these polyolefines, however, the additional difficulty arises that an appreciable proportion of the stabiliser is destroyed in the crosslinking process; on account of the high proportion of readily oxidisable tertiary carbon atoms which are located at the crosslinking positions and on account of the presence of long-lived radicals, the crosslinked polyolefines are more sensitive to oxidation than polymers which are not crosslinked.

These difficulties have only recently become acute. Formerly, cables tended only to be operated with relatively low temperatures in use or alternatively a shorter effective life of the polymer materials was accepted, so that the efficiency of the stabilisers which were used was adequate. Moreover, insulations stable up to 70"C were generally considered satisfactory for insulating materials for cables and conduits and, in addition, the direct contact with copper of the insulation was avoided either by introducing a foil or a lacquer as separator or by using tin-coated conductors; insulating materials which are filled with carbon black were and are also still used.

In order to be able to use insulations of different colours, it is necessary to use stabilisers which do not discolour the polymers being used. Metal deactivators which are based on bis-salicyloyl hydrazine have been employed for this purpose, as described in U.S. Patent Specification No, 3,849,492. Examples of these compounds which have proved effective for stabilising polyolefines against the damaging effect of transition metals have been bis-salicyloyl hydrazine derivatives with multiple alkyl-substitution or alkoxy-substitution.These compounds can also be used together with other additives, including anti-oxidants of the amino- and hydroxyaryl series, UV-absorbers and lightshielding agents, phosphites, nucleating agents, peroxide-destroying compounds, as well as plasticisers, antistatic agents, flame-proofing agents, pigments, carbon black, asbestos, glass fibres, kaolin, talc and blowing agents. A very large number of compounds are mentioned in US Patent Specification No. 3,849,492, both as regards the stabilisers proper and also the additives, such as anti-oxidants, so that an enormous number of possible combinations of components is feasible.

According to the present invention, there is provided a combined stabiliser composition for use in a polymer composition, the composition comprising unsubstituted N,N'-bis-salicyloyl hydrazine as metal deactivator and, as oxidation inhibitor, oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline.

The stabiliser combination of this invention has proved to be particularly effective in stabilising polymers which are in contact with copper. This stabiliser combination guarantees adequate protection of the polymers over long periods of time more particularly at elevated temperatures so that it is possible to dispense with the use of additional aids, such as separators, which are costly to provide or the costly tin-coating of copper conductors.

It has in fact been found surprisingly that it is just the unsubstituted bis-salicyloyl hydrazine, i.e. the parent compound of the stabilisers disclosed in US Patent Specification No. 3,849,492, which, when used in combination with specific oxidation inhibitors, has the maximum efficiency. This parent compound has the following chemical structure::

A large number of tests has shown that when the compound I is used with the aforementioned oxidation inhibitor, oligomeric 2,2,4-trimethyl- 1 ,2-dihydroquinoline, the effective life of a corresponding stabilised insulation at an operating temperature of 900C is many times better than the values which can be achieved with substituted derivatives of bis-salicyloyl hydrazine when used in combination with the oxidation inhibitor or when the unsubstituted compound is used in combination with other oxidation inhibitors than that to be used in accordance with this invention.

Ageing tests carried out on cross-linked polyethylene at temperatures between 180 and 1350C have yielded values which, when extrapolated according to Arrhenius, suggest that long-term stabilisation at 90"C, in fact stabilisation for far longer than 100 years, will be achieved when using the stabiliser combination of N,N'-bis-salicyloyl hydrazine and oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline. By comparison therewith, for example, when using oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline with that derivative of the parent compound I which is octoxy-substituted in the 5-positions or the 4-methoxy derivative, i.e. with N,N'-bis- (2-hydroxy-5-octoxybenzoyl) -hydrazine or N,N'-bis-(2-hydroxy-4-methoxybenzoyl)-hydrazine, values of from about 5 to 30 years only are obtained. The length of stabilisation which can be produced with the stabiliser combination according to the invention is accordingly a multiple of that achieved with such other combinations. Since the values determined for 90"C do not represent measurement values, the possibility cannot be excluded that they are subject to a certain uncertainty factor.If a sufficiently long period stability is to be guaranteed for commercial products, especially products for cables and conduits, with certainty, for at least 25 to 30 years, it is consequently necessary to look to those stabiliser combinations which promise, in addition, particularly high industrial safety, perhaps by being capable of use in smaller quantities than other combinations to achieve similar effect.

The stabiliser combination according to the invention offers the advantage that it is possible, if lower standards as regards the long-term stability (temperature and time) are to be accepted, to work with comparatively small concentrations which, not least of all, represents a saving in costs.

The stabiliser combination according to the invention also has the advantage that it does not cause any appreciable discoloration of the polymers. Furthermore, the effec tiveness of this stabiliser combination is also not adversely affected by the presence of fillers, for example chalk and carbon black, and also of pigment dyestuffs, i.e. metalcontaining dyestuffs. In addition, additives for intensifying the crosslinking added to the polymers, such as triallyl cyanurate, have only an insignificant influence on the long term stabilisation which can be produced with the stabiliser combination according to the invention.

Unsubstituted N,N'-bis-salicyloyl hydrazine is a compound which, in contrast to substitution products thereof, can industrially be manufactured relatively easily and cheaply. Furthermore, in contrast to other known metal deactivators, for example oxalic acid-bis-benzylidene hydrazide, N-salicyloyl-N'-salicylidene hydrazine and N,N'-bis-salicylidene ethylene diamine, this compound has the advantage of a substantially improved efficiency. The improved efficiency is more particularly of importance with polymers which are to be subjected to radical crosslinking. Conventionally employed stabilising additives, such as oxidation inhibitors and metal deactivators, exert an inhibiting influence on the crosslinking. However, it is now possible to employ considerably smaller concentrations of these additives when using stabiliser combinations embodying this invention.

The ratio by weight between metal deactivator and oxidation inhibitor in a stabiliser combination embodying this invention is preferably in the range from 7:3 to 3:7 and is more preferably about 1:1. When this stabiliser combination is added to polymers, the metal deactivator and oxidation inhibitor are each present in an amount preferably in the range of from 0.01 to 5.0% by weight, more preferably 0.1 to 1.0% by weight, related to the polymer.

A stabiliser combination embodying this invention may be employed for stabilising thermoplastic resins, thermoplastic or crosslinked elastomers and crosslinked thermoplastic resins, more especially crosslinked polyolefines. Such a stabiliser combination may also be used with resins which undergo crosslinking by virtue of their substituent groups, for example poly-urethanes, epoxide resins and unsaturated polyester resins (UP resins) to prevent the resin from undergoing degradation caused by thermal oxidation.The stabiliser combination is particularly effective when used with thermoplastic polymers, especially polyolefines, more particularly polyethylenes, polypropylenes, ethylene or propylene copolymers with one another and with other comonomers, such as vinyl acetate and ethyl acetate, polymer blends, which are based on polyethylenes or polypropylenes, and also polyoxymethylenes and polyamides. The stabiliser combination is of particular value when used with crosslinked polyolefines, in particular crosslinked polyethylenes, and especially polyethylene of low density, as well as with other crosslinked thermoplasts and elastomers based on olefines, such as ethylene-vinyl acetate, ethylene-propylene and ethylene-propylene-diene copolymers, as well as butyl rubber and natural rubber.The stabiliser combination may be used with polymers which are crosslinked chemically using free radical-producing compounds e.g. peroxides, as well as when radical cross-linking is achieved using ionising rays (a, y or X-ray radiation). In contrast to other stabilisers hitherto described, a positive effect in achieving stabilising against ageing is also obtained when using stabiliser combinations embodying this invention with polysiloxanes.

A stabliser combination embodying this invention can be advantageously used in all those cases where insulating materials which can be relatively easily oxidised are used in contact with copper and/or under extreme conditions of use, i.e. high temperatures and/or ionising radiation such that accelerated ageing due to oxidation of insulating materials which per Sed are stable is to be expected. The stabiliser combination can also be used when generally long exposure times have to be withstood without there being any essential loss of properties of the material which is used.

Polymers which contain a stabiliser combination embodying this invention are particularly suited to use as cable and conduit insulations in the power engineering and communications arts and also for moulded components and for insulations of structural components and machines. It is also possible for such polymers to be used in filled communication cables, since a stabiliser combination embodying this invention is not extracted by the conventional cable filling compositions from the insulating layer and as a consequence is able fully to maintain its excellent efficiency.

The following examples illustrate this invention.

The following metal deactivators which are based on bis-sallicyloyl hydrazine are used in the Examples for comparative purposes:

Metal deactivator Meaning of the substituents I R1= R2 = R3 = R4= H (Parent compound) II R1= R2= H; R3- R4= Cl III R1= R2= O CH3; R3 = R4 = H IV R1= R2= OC8H17; R3= R4= H V R1= R2= H; R3= R4= O C8H17 VI R1= R2= R3= H; R4= OC16H33 VII R1= R2= R3= H; R,= O Cl#Hs7 VIII R1= R2= H; R3= R4= O Cl8H3r Example 1.

a) Preparation of insulating composition 98 Parts by weight, of high-pressure polyethylene (d = 0.918 g/cc; MFI10,2= = 0.2) were plasticised in a kneader at a temperature of 140 C. 0.5 part by weight of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline, 0.5 parts by weight of metal deactivator and 1 part by weight of titanium dioxide were added to the plasticised polyethylene and homogenisation was carried out under a nitrogen atmosphere for 3 minutes at a temperature of from 140-150 C.

b) Preparation of specimens The mixture prepared by the procedure set out in a) was granulated and compressed at a temperature of 1800C into foils with a thickness of 0.3 mm, a pressing time of 1 minute being employed. A sandwich structure was formed by pressing together two pre-pressed foils with a thickness of 0.3 mm with a copper mesh (wire diameter: 0.11 mm; total thickness: 0.25 mm) freshly cleaned electrolytically disposed therebetween. Pressing was effected for two minutes at 1800C and yielded polyethylene/copper sandwich foils with a total thickness of 0.55 mm. These sandwich foils were crosslinked with electron beams in a dosage of 250 kJ/kg at ambient temperature.

c) Ageing test The effectiveness of the stabiliser combinations which were used was checked by ageing the polyethylene/copper sandwich foils in pure oxygen at temperatures of 135 and 1550C on the one hand and by ageing in a circulating air oven at temperatures of 135, 150, 165 and 1800C on the other hand. During the ageing in pure oxygen, the oxygen absorption of the foils was followed volumetrically and the time until autoxidation occurred was established as a so-called induction period, such autoxidation proceeding with a spontaneously occurring and quickly increasing absorption of oxygen by the foil. At least five specimens were aged simultaneously in each case, and an average of the values thereby obtained was then taken.

Table 1 sets out the induction periods established in respect of the specimens prepared by the procedure of Example 1 by the volumetric oxygen absorption method.

TABLE I

Induction period [hl at Metal deactivator 135"C 155"C I 1200 245 II 510 145 III 820 195 V 700 VI 610 180 VII 620 180 VIII 1 580 160 When the ageing was carried out in a circulating air oven, the time until the initiation of discoloration of the sandwich foils was established. The discoloration generally starts simultaneously at several positions; initially, greenish stains appear, and they quickly change to brown. After the occurrence of the first discoloration, the specimens were quickly and completely aged within a short time.

The induction periods which were obtained when using this latter method of ageing and established in respect of the specimens prepared by the procedure ol Example 1 are set out in Table 2. The induction periods which are indicated in Table 2 and in the following tables for 900C were determined by extrapolation according to Arrhenius.

TABLE 2

Induction period [h] at Metal Induction period (years) deactivator 180 C 165 C 150 C at 90 C I 80 1200 5500 140 II 140 450 1200 4000 30 III 130 430 1200 4000 30 IV 120 370 1 1000 3000 20 V 100 380 1100 3400 23 VIII 100 300 830 2600 16 Example 2.

a) Preparation of insulating composition 96.8 Parts by weight of high-pressure polyethylene (d = 0.918 g/cc; MFIl9U/2 = 0.2) were plasticised in a kneader at a temperature of 140"C. After adding 0.5 parts by weight of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline, 0.5 part by weight of metal deactivator and 1 part by weight of titanium dioxide, homogenisation was carried out under nitrogen for 3 minutes at a temperature from 14e150"C. 1.2 Parts by weight of 1,3-bis-(tert.-butyl-peroxyisopropyl) -benzene were then added and further homogenisation was carried out for 2 minutes.

b) Preparation of specimens The mixture obtained in a) was granulated and was pressed in the manner set out in Example ib to form polyethylene/copper sandwich foils. The crosslinking of the sandwich foils was effected by heating for 15 minutes in a press at a temperature of 1800C.

c) Ageing test Table 3 contains the induction periods obtained when volumetric oxygen absorption was effected at temperatures of 135 and 155 C.

TABLE 3

Induction period [hl at Metal deactivator 135"C 155"C I 1100 220 II 700 190 III 820 220 In Table 4 are set out the induction periods obtained when ageing in a circulating air oven was effected.

TABLE 4

Induction period [h] at Metal Induction period (years) deactivator 1800C 165 C 150 C 135 C at 90C I 65 240 1000 4700 110 II 120 380 1100 3750 27 III 140 430 1150 3700 25 IV 120 320 . 1000 3200 20 V 25 70 200 700 5 VI 30 85 280 900 6 VII 30 90 290 920 6 VIII 25 70 190 700 5 Reference will now be made to Figure 1 of the accompanying drawings in which the results of the aforesaid ageing rests (Examples 1 and 2) in the circulating air oven are presented in the form of a graph. The results were established when using the stabiliser combination according to the invention with unsubstituted N,N'-bis-salicyloyl hydrazine and when using mixtures containing derivatives of this compound.

Curve 10 shows the behaviour of the specimen crosslinked by irradiation in the manner set out in Example 1 when using the stabiliser combination according to the invention, i.e. with the metal deactivator I and oligomeric 2,2,4-trimethyl-1, 2-dihydroquinoline. The results of experiments obtained when effecting peroxide-crosslinking (corresponding to Example 2) are set out in curve 11. Curves 12 and 13 show in corresponding manner the results which were obtained when using the metal deactivator III in the cross-linking procedures of Example 1 and 2 respectively.

Example 3.

98.4 Parts by weight of high-pressure polyethylene (d = 0.918 g/cc; MFIIDo/2,=0.2) were mixed as in Example la with 0.3 parts by weight of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline, 0.3 part by weight of metal deactivator and 1 part by weight of titanium dioxide and polyethylene/copper sandwich foils, which were crosslinked at room temperature with electron beams in a dosage of 250 kJ/kg, were obtained from this mixture in accordance with Example ib.

Table 5 contains the induction periods established in respect of such foils when subjected to the volumetric oxygen absorption test.

TABLE 5

Induction period [h] at Metal deactivator 135 C 155 C I 700 170 V 400 100 VI 450 120 VII 450 120 VIII 350 90 Example 4.

97.2 Parts by weight of high-pressure polyethylene (d= 0.918 g/cc; MFIl0/2 = 0.2) were mixed with 0.3 part by weight of oligomeric 2,2,4-trimethyl-1,2dihydroquinoline, 0.3 part by weight of metal deactivator, 1 part by weight of titanium dioxide and 1.2 parts by weight of 1,3-bis-(tert.-butyl-peroxyisopropyl)-benzene, in analogous manner to Example 2, and crosslinked polyethylene/copper sandwich foils were produced therefrom, these foils being subjected to the various ageing tests.

Table 6 sets out the induction periods determined by the volumetric oxygen absorption method.

TABLE 6

Induction period [h] at Metal deactivator 135"C 1550C I 500 130 V 80 20 VII 120 40 VIII 60 15 The induction periods established when using the ageing method in the circulating air oven are set out in Table 7.

TABLE 7

Induction period [hl at Metal Induction period [years] deactivator 180 C 165 C 150 C 135 C at 90 C I 37 130 500 2100 35 V 16 30 110 370 3 VIII 12 30 90 290 2 Reference will now be made to Figure 2 of the accompanying drawings in which the results of tests carried out in connection with peroxide-crosslinked specimens produced in Example 4, are set out in the form of graphs the ageing tests having been effected in the circulating air oven.

Curve 20 shows the behaviour of the specimen with the stabiliser combination according to the invention. Curve 21 shows the results which were obtained when using the metal deactivator V. When curves 20 and 21 are compared, it is seen that the ditferences in the long-term stabilisation between the unsubstituted N,N'-bis-salicyloylhydrazine and its substitution product, i.e. the 5-octoxy derivative, are considerable; this improvement shows a ten-fold increase in the length of the stabilisation time.

Example 5.

98 parts by weight of high-pressure polyethylene (d=0.918 g/cc; MFI1012--0.2) were mixed with 0.5 part by weight of metal deactivator I, i.e. N,N'-bis-salicyloyl hydrazine, 0.5 part by weight of an oxidation inhibitor and 1 part by weight of titanium oxide, as in Example 1, and polyethylene/copper sandwich foils were produced from the mixture thereby obtained, these foils being crosslinked at ambient temperature with electron beams in a dosage of 250 kJ/kg.

The following selection of oxidation inhibitors was used for comparative purposes to show the particular efficacy of N,N'-bis-salicyloyl hydrazine. The oxidation inhibitors were chosen because of their characteristically different stabilising functional groups as well as their different molecular weight, all of these compounds generally being considered to be particularly effective stabilisers; 1: oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline (mean molecular weight: 510); 2:N-isopropyl-N'-phenyl-p-phenylene diamine (molecu!ar weight: 226); 3: N,N'-diphenylop-phenylene diamine (molecular weight: 260); 4: 3,5-ditert.-butyl-4-hydroxyphenyl propionic acid octadecyl ester (molecular weight: 530); 5: 2,4 - bis - (3,5- ditert. - butyl - 4 - hydroxyphenoxy) - 6 - octylthio - 1,3,5- s-triazine (molecular weight: 665); 6: ester of 3,S-ditert.-butyl-4-hydroxyphenyl propionic acid with pentaerythritol (molecular weight: 1176); 7: monomeric 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (molecular weight: 217).

The induction periods which were obtained by ageing in the circulating air oven test at temperatures ranging from 135 to 1800C, and when extrapolated to 900C, are set out in Table 8.

TABLE 8

Induction period [h] at Oxidation Induction period (years) inhibitor 180 C 165 C 146 C 135 C at 90 C 1 80 300 1900 5500 1 3 56 210 1380 4200 90 4 - 28 95 500 1350 18 5 30 120 700 1700 30 6 50 185 1150 3200 60 7 8 24 75 250 2 Since it is known that stabilisers are exuded from polymer material and may be lost from the surface of a test specimen, pre-ageing operations were carried out on corresponding specimens in a circulating air oven at 60"C, so as to establish whether and to what extent this effect occurs. In this connection, specimens were removed at certain time intervals and the induction periods for them were established at 1659C.

Set out in Table 9 are the induction periods which were obtained after a preageing of 2, 4, 6 or 8 months.

TABLE 9

Induction period [h] at 165 C after pre-ageing Oxidation Decrease in the inhibitor 0mth. 2mths. 4mths. 6mths. 8mths. induction period % 1 300 295 302 300 297 1 2 190 174 164 157 153 3 210 200 190 182 176 12 4 95 80 53 47 44 54 5 120 105 96 i 83 70 42 6 185 180 180 174 168 10 As will be apparent from Table 8, the combination of oligomeric 2,2,4-trimethyl1,2-dihydroquinoline (oxidation inhibitor 1) and metal deactivator I proved to be the most effective. In addition, it can be seen from Table 9 that the efficiency of this oxidation inhibitor is not adversely affected by a pre-ageing treatment, as is the case with the other oxidation inhibitors. These oxidation inhibitors obviously migrate from the polymers. The fact that this migration does not occur with oligomeric 2,2,4-trimethyl1,2-dihydroquinoline must be considered as surprising, since this compound possesses a substantially lower molecular weight than some of the other oxidation inhibitors which were investigated and which themselves undergo loss by exudation, although generally to a lower extent than the oxidation stabilisers of lower molecular weight.

Example 6.

97 parts by weight of high-pressure polyethylene (d=0.918 g/cc; MFI190,=0.2) were mixed by the procedure of Example 1 with 0.5 part by weight of oligomeric 2,2,4trimethyl-1,2-dihydroquinoline, 0.5 parts by weight of N,N'-bis-salicyloyl-hydrazine, 1 part by weight of euthylene blue E (a copper-phthalocyanine complex) and 1 part by weight of titanium dioxide and polyethylene/copper sandwich foils were produced therefrom, these foils being cross-linked at room temperature with electron beams with a dosage of 250 kJ/kg.

The induction periods which were established in respect of such specimens by ageing in a circulating air oven together with the value extrapolated to 900C are set out in Table 10.

TABLE 10

Induction period [yearsl Induction period [hl at at 90 C 1800C j 165 C j 1500C 135 C < 1100 4300 110 Example 7.

95 Parts by weight of high-pressure polyethylene (d=0.918 g/cc; MFI1.98/2!=0.2) were mixed by the procedure set out in Example 1, with 0.5 parts by weight of N,N'bis-salicyloyl-hydrazine, 0.5 part by weight of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline, 2 parts by weight of triallyl cyanurate as agent for intensifying the crosslinking, 1 part by weight of euthylene blue E and 1 part by weight of titanium dioxide and polyethylene/copper sandwich foils were prepared from the mixture obtained, the foils being crosslinked at ambient temperature with electron beams in a dosage of 250 kJ/kg and aged in a circulating air oven.

The induction period values obtained in this case are set out in Table 11.

TABLE 11

Induction period [h, at Induction period [years] 180 C 165 C 1500C 135 C 90 C 24 140 600 2500 70 Example 8.

Mixtures of the following compositions were produced at a temperature from 120 to 1300C by the procedure of Example la: a) 98 parts by weight of ethylene-vinyl acetate copolymer (d 0.932 g/cc; MFIlgo/2=216) with a vinyl acetate content of about 10 to 15% by weight, 0.5 part by weight of N,N'-bis-salicyloyl-hydrazine, 0.5 part by weight of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline and 1.0 part by weight of titanium dioxide; b) 95 parts by weight of the aforesaid ethylene-vinyl acetate copolymer, 0.5 part by weight of N,N'-bis-saiicyloyl-hydrazine, 0.5 part by weight of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline, 1 part by weight of titanium dioxide, 2 parts by weight of triallyl cyanurate and 1 part by weight of euthylene blue E;; c) 61 parts by weight of the aforesaid ethylene-vinyl acetate copolymer, 0.3 part by weight of N,N'-bis-salicyloyl-hydrazine, 0.3 part by weight of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline, 36.6 parts by weight of chalk, 1.2 parts by weight of triallyl cyanurate and 0.6 part by weight of euthylene blue E.

Following the procedure of Example 1b, specimens were produced from these mixtures by pressing for 5 minutes at 1300 C and crosslinking at ambient temperature with electron beams in a dosage of 200 kJ/kg.

The induction periods established by ageing in the circulating air oven are set out in Table 12.

TABLE 12

Induction period [h] at Induction period [years] Mixture 180 C 165 C 150 C 135 C at 90 C a 65 220 1070 3500 60 b 55 200 900 3300 50 c 35 120 450 1800 30 Example 9.

Following the procedure of Example la, mixtures having the following compositions were prepared at a temperature from 220 to 230 C; a) 99 parts by weight of a stabilised commercially available form of polypropylene (d= 0.947 g/cc; MFII,,o/2 = 1) and 1 part by weight of titanium dioxide; b) 98 parts by weight of the previously mentioned polypropylene, from which the stabilisers contained therein were extracted by cold extraction for 70 hours using diethyl ether, 0.5 part by weight of N.N'-bis-salicyloyl-hydrazine, 0.5 part by weight of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline and 1 part by weight of titanium dioxide.

Following the procedure of Example 1b, polypropylene/copper sandwich foils were produced from these mixtures by pressing for 2 minutes at 230 C. Induction periods were established for these foils by ageing in a circulating air oven at 1500C and are set out in Table 13.

TABLE 13

Mixture Induction period [h] at 150 C a 40 500C b 950 Example 10.

Following the procedure of Example la, mixtures of the following composition were prepared at a temperature of from 220 to 230"C; a) 99 parts by weight of a stabilised polyblend based on polypropylene/polyethylene (d= 0.91 g/cc; MFI1s,o/, = 1.8) - the product Hostalen LP 233 (Hostalen is a Registered Trade Mark) - and 1 part by weight of titanium dioxide; b) 98 parts by weight of the aforementioned polyblend, from which the stabilisers contained therein had been extracted by cold extraction for 70 hours with diethyl ether, 0.5 part by weight of N,N'-bis-salicyloyl-hydrazine, 0.5 part by weight of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline and 1 part by weight of titanium dioxide.

Following the procedure of Example ib, polyblend/copper sandwich foils were produced from these mixtures by pressing for 2 minutes at 230"C. The induction periods established by ageing in the circulating air oven are set out in Table 14.

TABLE 14

Mixture Induction period [h] at 1500C a 50 b 1000 WHAT WE CLAIM IS: 1. A combined stabilizer composition for use in a polymer composition, the composition comprising unsubstituted N,N'-bis-salicyloyl-hydrazine as metal deactivator and, as oxidation inhibitor, oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline.

2. A composition as claimed in Claim 1, wherein the metal deactivator and oxidation inhibitor are present in a ratio by weight of from 7:3 to 3:7.

3. A composition as claimed in Claim 2, wherein the metal deactivator and oxidation inhibitor are present in a ratio by weight of approximately 1:1.

4. A combined stabilizer composition as claimed in Claim 1, substantially as described in any one of the foregoing Examples.

5. A polymer composition which comprises a combined stabilizer composition as claimed in any one of the preceding claims, whose components, added separately or together, are admixed with a polymeric material.

6. A polymer composition as claimed in Claim 5, wherein the metal deactivator and oxidation inhibitor are each present in an amount of from 0.01 to 5.0% by weight of the polymeric material.

7. A polymer composition as claimed in Claim 6, wherein the metal deactivator and oxidation inhibitor are each present in an amount of from 0.1 to 1.0% by weight of the polymeric material.

8. A polymer composition as claimed in any one of Claims 5 to 7, wherein the polymeric material is a thermoplastic plastics material or an elastomer.

9. A polymer composition as claimed in Claim 8, wherein the polymeric material is cross-linked.

10. A polymer composition as claimed in claim 8 or 9, wherein the plastics material is a polyolefin or olefine copolymer.

11. A polymer composition as claimed in Claim 10, wherein the plastics material is polyethylene, polypropylene, an ethylene-propylene copolymer or a copolymer of ethylene or propylene with vinyl acetate.

12. A polymer composition as claimed in Ciaim 11 wherein the plastics material is cross-linked polyethylene.

13. A polymer composition as claimed in Claim 5, substantially as described in any one of the foregoing Examples.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (15)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE 13 Mixture Induction period [h] at 150 C a 40 500C b 950 Example 10. Following the procedure of Example la, mixtures of the following composition were prepared at a temperature of from 220 to 230"C; a) 99 parts by weight of a stabilised polyblend based on polypropylene/polyethylene (d= 0.91 g/cc; MFI1s,o/, = 1.8) - the product Hostalen LP 233 (Hostalen is a Registered Trade Mark) - and 1 part by weight of titanium dioxide; b) 98 parts by weight of the aforementioned polyblend, from which the stabilisers contained therein had been extracted by cold extraction for 70 hours with diethyl ether, 0.5 part by weight of N,N'-bis-salicyloyl-hydrazine, 0.5 part by weight of oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline and 1 part by weight of titanium dioxide. Following the procedure of Example ib, polyblend/copper sandwich foils were produced from these mixtures by pressing for 2 minutes at 230"C. The induction periods established by ageing in the circulating air oven are set out in Table 14. TABLE 14 Mixture Induction period [h] at 1500C a 50 b 1000 WHAT WE CLAIM IS:

1. A combined stabilizer composition for use in a polymer composition, the composition comprising unsubstituted N,N'-bis-salicyloyl-hydrazine as metal deactivator and, as oxidation inhibitor, oligomeric 2,2,4-trimethyl-1,2-dihydroquinoline.

2. A composition as claimed in Claim 1, wherein the metal deactivator and oxidation inhibitor are present in a ratio by weight of from 7:3 to 3:7.

3. A composition as claimed in Claim 2, wherein the metal deactivator and oxidation inhibitor are present in a ratio by weight of approximately 1:1.

4. A combined stabilizer composition as claimed in Claim 1, substantially as described in any one of the foregoing Examples.

5. A polymer composition which comprises a combined stabilizer composition as claimed in any one of the preceding claims, whose components, added separately or together, are admixed with a polymeric material.

6. A polymer composition as claimed in Claim 5, wherein the metal deactivator and oxidation inhibitor are each present in an amount of from 0.01 to 5.0% by weight of the polymeric material.

7. A polymer composition as claimed in Claim 6, wherein the metal deactivator and oxidation inhibitor are each present in an amount of from 0.1 to 1.0% by weight of the polymeric material.

8. A polymer composition as claimed in any one of Claims 5 to 7, wherein the polymeric material is a thermoplastic plastics material or an elastomer.

9. A polymer composition as claimed in Claim 8, wherein the polymeric material is cross-linked.

10. A polymer composition as claimed in claim 8 or 9, wherein the plastics material is a polyolefin or olefine copolymer.

11. A polymer composition as claimed in Claim 10, wherein the plastics material is polyethylene, polypropylene, an ethylene-propylene copolymer or a copolymer of ethylene or propylene with vinyl acetate.

12. A polymer composition as claimed in Ciaim 11 wherein the plastics material is cross-linked polyethylene.

13. A polymer composition as claimed in Claim 5, substantially as described in any one of the foregoing Examples.

14. A shaped plastics product which is formed from a polymer composition as

claimed in any one of Claims 5 to 13 which polymer composition is in contact with metallic copper.

15. A product as claimed in Claim 13, wherein the polymer composition is a cable insulation or conduit-forming material.