GB2110697A

GB2110697A - Vinyl chloride polymer compositions

Info

Publication number: GB2110697A
Application number: GB08231465A
Authority: GB
Inventors: Howard Bernard Silver; David Bernard Thomas
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1981-11-07
Filing date: 1982-11-03
Publication date: 1983-06-22
Also published as: GB2110697B

Abstract

A thermal stabiliser for poly vinyl chloride compositions comprises a basic zinc carboxylate having the empirical formula (RCOO)6Zn4O where R is a branched chain alkyl, cycloalkyl, aryl, aralkyl or alkaryl group, e.g. 2 ethyl hexyl. The carboxylate has a tetrahedral structure with the four zinc atoms at the corners, the oxygen atom at the centre and the six carboxylate groups arranged along the sides. The basic zinc salt is preferably used in combination with another metal carboxylate e.g. calcium stearate.

Description

SPECIFICATION Vinyl chloride polymer compositions The present invention relates to stabilised vinyl chloride polymer compositions containing basic zinc carboxylates.

Vinyl chloride polymers, are widely used in the manufacture of plastics articles. They may be homopolymers, or copolymers with other copolymerisable monomers, and may be used plasticised or unplasticised. Vinyl chloride polymers tend to degrade when subjected to heat and it is therefore necessary to add a stabiliser to the polymer to retard this degradation.

Certain metal carboxylate mixtures, e.g. cadmium/barium/zinc carboxylate compounds and cadmium/zinc carboxylate mixtures are known as thermal stabilisers for polyvinyl chloride. However, the toxicity of cadmium compounds has led to attempts to stabilise polyvinyl chloride with additives which do not contain cadmium. Additives comprising calcium and zinc carboxylates have been used as stabilisers but they are generally less effective as thermal stabilisers than additives containing cadmium.

The applicants have found that a basic zinc carboxylate having a particular structure is an effective thermal stabiliser for poly vinyl chloride, particularly when used in combination with another metal carboxylate such as, for example, calcium stearate. The basic zinc carboxylate is a more effective thermal stabiliser than conventional zinc carboxylates.

According to the present invention a composition comprising a vinyl chloride polymer and a zinc carboxylate as a thermal stabiliser is characterised in that the zinc carboxylate is a basic zinc carboxylate having the emperical formula (RCO0)6Zn40 where R is a branched chain alkyl, cycloalkyl, aryl, aralkyl, or alkaryl group, the salt having a tetrahedral structure with the four zinc atoms at the corners, the oxygen atom at the centre and the six carboxylate groups arranged along the sides.

The production of basic zinc salts of the above structure is disclosed in British Patent No.

1142195.

The vinyl chloride polymer may be a homopolymer or a copolymer with another copolymerisable monomer e.g. vinyl acetate. Where a copolymer is used it may for example contain up to 30% by weight of the comonomer.

The vinyl chloride polymer may be a polymer made by mass, suspension, microsuspension, or emulsion polymerisation.

The zinc salts which may be used in the process of the present invention are preferably those in which R in the formula (RCO0)6Zn40 contains not more than 24 carbon atoms and not less than 3.

Preferably R is a branched chain alkyl group having not more than 1 8 and not less than 5 carbon atoms. R may for example be 2-ethyl hexyl.

The quantity of zinc salt used in the compositions of the present inventions may vary over a moderately wide range for example from 0.2 to 5% by weight of the vinyl chloride polymer, more preferably 0.5 to 2.5%.

The zinc salt is preferably used together with other metal carboxylates e.g. calcium carboxylate.

Suitable calcium carboxylates include calcium salts of fatty acids having from 10 to 22 carbon atoms in the molecule, such as calcium stearate.

The quantity of calcium salt used may vary over a moderately wide range for example 0.2% by weight to 5% by weight based on weight of vinyl chloride polymer.

The vinyl chloride polymer composition may contain the usual materials conventionally used in making vinyl chloride polymer compounds e.g. fillers, pigments, process aids, impact modifiers.

Although the basic zinc carboxylate of the present invention has been referred to as a thermal stabiliser throughout this specification it has also been found that the compound may act as an activator for the blowing agent in the production of foamed polyvinyl chloride i.e. it can lower the temperature at which the foaming agent azodicarbonamide decompses to produce nitrogen.

The invention will now be illustrated by reference to the following Examples.

Comparative Test A polyvinyl chloride blend was prepared from the following ingredients: parts by weight Vinyl chloride homopolymer made by the suspension process and having an ISO viscosity number of about 110 100 Dioctyl adipate 23 Commercial heat stabiliser (a blend of Ca and Zn salts of long chain, fatty acids sold as Lankromark LZ 330) 3.3 Glyceryl Mono-oleate (sold as Estol 651) 0.1 Wax (sold as Glokem D2S) 1.0 Epoxidised Soyabean Oil (sold as Paraplex G 62) 5.5 The ingredients were mixed together on a 'Kenwood' ('Kenwood' is a Trade Mark) mixer and then milled to give a clear PVC flexible sheet. The sheet was cut into discs of diameter 25.4 mm (1 inch) which were placed in an oven at 1 800 C. Discs were removed from the oven at 10 minute intervals for up to 2 hours.The colour of the discs changed from the initial water-white colour to dark brown as heating continued.

Example 1 An experiment was carried out as in the Comparative Test except that the commercial stabiiiser was replaced by a mixture of 1.65 parts by weight of the basic zinc 2-ethyl hexanoate, and 1.65 parts by weight of calcium stearate.

Example 2 An experiment was carried out as in Example 1 except that the quantity of basic zinc salt was 2.0 parts by weight and the quantity of calcium stearate was 1.3 parts by weight.

A comparison of the discs showed that degradation (as shown by discoloration) proceeded more slowly with the compositions of the invention than when the commercial stabiliser was used. The composition of Example 1 was slightly better than the composition of Example 2.

The basic zinc 2-ethyl hexanoate used in Examples 1 and 2 had an emperical formula (RCO0)6Zn40 where R is a 2-ethyl hexyl group. The compound had a tetrahedral structure with the four ziiic atoms at the corners, the oxygen atom at the centre and the six 2-ethyl hexyl groups arranged along the sides. The preparation of the basic zinc carboxylate is disclosed in British Patent No.

1142195.

Claims

1. A composition comprising a vinyl chloride polymer and a zinc carboxylate, as a thermal stabiliser, characterised in that the zinc carboxylate is a basic zinc carboxylate having the empirical formula (RCO0)6 Zn40 where R is a branched chain alkyl, cycloalkyl, aryl, aralkyl or alkaryl group, the salt having a tetrahedral structure with the four zinc atoms at the corners, the oxygen atom at the centre and the six carboxylate groups arranged along the sides.

2. A composition as claimed in claim 1 characterised in that the number of carbon atoms in the group R of the basic zinc salt is from 3 to 24.

3. A composition as claimed in claim 2 characterised in that R is a branched chain alkyl group having from 5 to 18 carbon atoms.

4. A composition as claimed in claim 3 characterised in that R is 2 ethyl hexyl.

5. A composition as claimed in any of claims 1 to 4 characterised in that the amount of the basic zinc carboxylate is in the range 0.2 to 5% by weight of the vinyl chloride polymer.

6. A composition as claimed in claim 5 characterised in that the amount of the basic zinc carboxylate is in the range 0.5 to 2.5% by weight of the vinyl chloride polymer.

7. A composition as claimed in any of claims 1 to 6 characterised in that the composition also contains a calcium carboxylate having from 10 to 22 carbon atoms.

8. A composition as claimed in claim 7 characterised in that the calcium carboxylate is calcium stearate.

9. A composition as claimed in either of claims 7 or 8 characterised in that the amount of calcium carboxylate is in the range 0.2 to 5% by weight of the vinyl chloride polymer.

10. A composition substantially as described with reference ho the Examples.