IE46179B1 - Composition for flameproofing plastics - Google Patents

Abstract

The flame-retardant composition intended for use in plastics consists of 50 to 95 % by weight of red phosphorus powder coated with 5 to 50 % by weight, relative to the total weight of the mixture, of a saturated polyester which has a melting point of between 50 and 90 DEG C and a molecular mass lower than 10,000. These flame-retardant compositions do not give off toxic products when used with plastics intended for the manufacture of shaped articles.

Description

The present invention relates to compositions for flameproofing plastics, which compositions are based on red phosphorus.

Numerous patents cover the use of phosphorus for 5 the flameproofing of plastics; in fact, red phosphorus is a very good flameproofing agent. For a given effect, it is necessary to employ smaller amounts of phosphorus than, for example, of halogen derivatives.

Furthermore, the use of phosphorus gives better 10 mechanical properties, and does not interfere with the electrical properties, of the plasties into which it is incorporated.

However, the use of phosphorus is limited by the dangers encountered, namely pollution hazards, and difficulties in using the material completely safely. In ¢fact, the presence of traces of water in almost all polymers causes, during the heating required for processing these polymers, the formation of phosphine, which is very toxic and which ignites spontaneously in air.

Andreev and Kavtaradae have found that it is possible to oxidise phosphine in the presence of copper oxide (see Reports of the Academy of Sciences of the U.S.S.R. 1948 LX No. 7). However, copper oxide also oxidises the red phosphorus. to overcome these disadvantages it has been proposed, (see French Patent No. 2,074,394), to incorporate into the thermoplastic, which may be reinforced with glass fibres, red phosphorus impregnated with a lactam containing 4 to 12 carbon atoms, for example caprolactam, in a proportion of 1 to 20% relative to the weight of the polymer.

However, the essential disadvantage of this process is the hydroscopicity of the lactams, which is such that the presence of water in the mixture causes the formation of phosphine, which is very toxic and ignites spontaneously in air, especially at the temperatures at which the polymers are processed.

German Patent Specification No. 2,308,104 discloses thermoplastic compositions flameproofed with red phosphorus and containing metal oxides to prevent any evolution of phosphine during storage at ambient temperature. However, the addition of metal oxides is insufficient to prevent the evolution of phosphine produced at a high temperature.

Various products such as waxes and metal salts of fatty acids have been proposed for coating the particles of red phosphorus and insulating them from any contact with, in particular, copper oxide, thus reducing the evolution of phosphine. However, the presence of various coating agents can interfere with the mechanical properties of the shaped articles obtained from these compositions.

It is therefore necessary to find a simple means which allows red phosphorus to be used without any phosphine being evolved, especially when the plastics are intended for the production of shaped articles, and without deterioration of the mechanical properties of the articles.

It has now been found, according to the present invention, that this can substantially be achieved by using compositions (suitable for the flameproofing of plastics) which contain: a) from 50 to 95% by weight of red phosphorus in the form of a powder generally having a mean particle size not exceeding 200 μ, and b) from 5 to 50% by weight of a saturated thermoplastic polyester having a melting point of at least 50°C but below 100°C, generally from 50° to 90°C, and a molecular weight not exceeding 10,000 and preferably from 500 to 2,000.

Red phosphorus, as used herein, means all the coloured allotropic varieties of phosphorus which are sold commercially under the name of red phosphorus, and which can contain up to, say, 3% of metal oxides or metal salts as stabilisers.

This red phosphorus must be in the form of a powder, generally having a mean particle diameter not exceeding 200 μ. The use of particles of only a few microns in diameter makes it possible to flameproof spun articles for textile use.

The polyesters which are suitable according to the invention are well known, and are solid at ambient temperature and have a melting point of at least 50°C but below 100°C, preferably from 50° to 90°C. The degree of polymerisation is _ - 4 46179 low or medium, preferably corresponding to a molecular weight of from 500 to 2,000. These polyesters can be obtained by polycondensation of aliphatic diols with one or more aliphatic, cycloaliphatic or aromatic dicarboxylic acids. Such polyesters are described in V.V. Korshak and S.V. Vinogradova Polyesters Pergamon Press, 1965.

The composition according to the invention can be prepared simply by mixing the two components whilst cold and then heating the mixture to a temperature slightly above the melting point of the polyester. It is found that the polyester homogeneously coats the phosphorus particles.

The use of various polymers mixed with the polyesters described above is possible. In particular, mixtures with phenol-formaldehyde prepolycondensates of the NOVOLAC type may be mentioned.

The polyesters can also be deposited on the surface of the phosphorus particles. For this purpose, it is possible to employ numerous encapsulation processes, such as those described in Encyclopaedia of Polymer Science and Technology, volume 8, page 179 et seg, Interscisnee Publishers. These processes are essentially of a chemical or a physical nature. Amongst the commonest processes there may be mentioned coacervation in an aqueous phase or interfacial coacervation, precipitation in an organic phase by addition of a non-solvent, dry spraying, the use of a fluidised bed, interfacial polymerisation or polymerisation in situ in the vapour phase or - 5 179 in the moist phase, vacuum deposition and electrostatic deposition, as well as numerous other processes based on phase separation methods or interfacial reaction methods.

In order that the protection provided by the polyester shall be satisfactory, the amount employed must be from 5 and 50% by weight relative to the mixture of red phosphorus and polyester.

It is furthermore known that the addition of metal oxides or metal salts stabilises red phosphorus; rod phosphorus sold commercially usually contains these additives. The addition of metal oxides, which makes it possible to reduce the possible evolution of phosphine, is permitted for the compositions of this invention. The metal oxides which give the best results are the oxides of copper, zinc, silver, iron, antimony, vanadium, tin, titanium, cadmium and magnesium, but the use of copper oxide and/or of cadmium oxide is preferred.

The amounts of metal oxide employed can vary in accordance with the amount of polyester used, in accordance with the conditions under which the synthetic resins are employed, as well as in accordance with the nature of these synthetic resins. Usually, up to 100% by weight, relative to the red phosphorus, of metal oxide can be used.

Very many synthetic polymers are used for obtaining shaped articles which more and more frequently have to be flameproofed. Numerous compositions based on thermoplastic 46178 polymers, thermosetting polymers or elastomers can be flameproofed using the compositions of this invention.

Amongst the thermoplastic polymers there may be mentioned the polyolefines, such as high density or low density polyethylene, polypropylene, polyfluoroethylenes and ethylene-propylene copolymers, the polyvinyl compounds such as polyvinyl chloride or vinyl chloride copolymers, the polyamides, such as polyhexamethylene adipamide, polycaprolactam, polyhexamethylene sebacamide, polyundeeanamicte, polylauryllactam, polyhexamethylene azelamide and polyhexamethylene dodecanediamide, the saturated polyesters such as poly(ethylene glycol terephthalate) or poly(butylene glycol terephthalate), the polyacetals, the polyacrylics, such as polymethyl methacrylate, the cellulosic esters, the polyurethanes or the polyamide-imides, the polystyrenes and the acrylonitrile-butadiene-styrene copolymers.

Amongst the thermosetting polymers there may be mentioned the phenolic resins, the aminoplasts, the unsaturated polyesters, the polyepoxides and the polyimides.

Various elastomers can also be flameproofed using the compositions according to the invention. As examples there may be mentioned natural or synthetic rubbers, silicones and polyurethane elastomers.

All these plastics, in particular when they are intended for producing shaped articles, are usually employed with various adjuvants, for example, reinforcing fillers - 7 46179 such as glass fibres, fillers intended Lo impart specific characteristics to the shaped articles, or inert fillers such as kaolin or talc, antioxidants, various stabilisers, dyestuffs or pigments. The flameproofing composition is usually used in an amount from 0.2 to 20% by weight based on the weight of the plastic to obtain a suitable flameproofed effect.

The use of encapsulated particles of red phosphorus offers numerous advantages amongst which there may be mentioned ease of handling before and during introduction into the polymer compositions, the reduction of the hazards of pollution during the preparation of the compounds and above all the absence of evolution of phosphine during processing, particularly when working at temperatures above 200°C.

In the Examples which follow and which further illustrate the present invention the polymer chosen for flameproofing was a polyamide 6-6, the moisture uptake of which is, with the exception of the cellulosics, amongst the highest exhibited by polymers and gives rise, on heating and in the presence of red phosphorus, to the greatest evolution of phosphine.

EXAMPLE 1 660 g of a red phosphorus powder having a mean particle size of 20 to 30 are mixed with 400 g of a poly(ethylene glycol sebacate) having a particle size of less than 500 μ, a molecular weight of about 3650, and a melting point of about 72°C. These powders are mixed intimately by agitation on rollers for 20 minutes. The mixture is then poured, to a thickness of about 1 cm, onto plates covered with aluminium foil. The material is placed in an oven at 120°C for 3 hours under a pressure of 30 mm of mercury. Plates are obtained, which are broken into fragments of size between 300 μ and 6 mm. It is found that the broken edge does not liberate red phosphorus powder on rubbing and that the phosphorus particles have been coated.

The following composition is prepared by simple mixing in a mechanical mixer: 4,412.5 g of poly(hexamethylene adipamide) having a mean molecular weight of 20,000 and a viscosity index, determined in accordance with standard specification ISO R 307, of 145, 12.5 g of copper oxide and 575 g of the mixture of red phosphorus and polyester prepared above (mixture A).

This composition is mixed tor 10 minutes at 16 rpm and is then introduced into an extruder, and a strand is extruded.

A laboratory single-screw extruder, in which the screw has a length of 900 mm and a diameter of 45 mm, is used. This extruder is equipped with a cylindrical die having a diameter of 3.5 mm. The barrel temperatures are as follows: 255°C at the material inlet, 270°C - 275°C at the centre and 26O°C at the die. The screw revolves at 45 rpm, giving a flow rate of 15 kg/hour.

Throughout the operation, tests to detect the possible presence of phosphine is carried out, in different parts of the extruder, by means of a DRAEGER CH 31,101 tube. Equally, attempts are made to detect phosphine when breaking the strand which has just been extruded and is still hot.

All these tests are negative.

EXAMPLE 2 The procedure indicated in Example 1 is employed, but the following composition is prepared by mixing: 4,375 g of a compound based on poly(hexamethylene adipamide) having a mean molecular weight of 20,000 and a viscosity index of 145, and containing 30% of glass fibres, 525 g of mixture A and 100 g of cadmium oxide.

This composition is mixed for 10 minutes at 16 rpm and then introduced into the extruder.

The same sampling of air by means of the DRAEGER tube above the die, the feed hopper and the granulator, permit the absence of phosphine to be established.

EXAMPLE 3 The procedure described in Example 1 is followed, but the 575 g of the 60/40 mixture of red phosphorus and polyester are replaced by 575 g of a 60/40 mixture of red phosphorus and polyester prepared as in Example 1, but with a poly(ethylene glycol adipate) having a melting point of 65°C and a mean molecular weight of 2,000 (mixture B).

No evolution whatsoever of phosphine is observed. - 10 46179 EXAMPLE 4 The procedure described in Example 2 is followed, but with 525 g of mixture B. 'Ihe evolution of phosphine is less than 0.1 ppm.

EXAMPLE 5 The procedure indicated in Example 1 is followed, but with a different charge, namely 4,495 g of poly(hexamethylene adipamide), 492.5 g of a 70/30 mixture of red phosphorus and poly(ethylene glycol sebacate) (mixture C) and 12.5 g of copper oxide.

No evolution whatsoever of phosphine is observed. EXAMPLE 6 The procedure indicated in Example 1 is followed, with a charge of 4,450 g of poly(hexamethylene adipamide) compound, 450 g of mixture C and 100 g of cadmium oxide.

No evolution whatsoever of phosphine is observed.

Claims (10)

1. A flameproofing composition which comprises: a) from 50 to 95% by weight of red phosphorus (as hereinbefore defined) in the form of a powder and 5 b) from 5 to 50% by weight of a saturated thermoplastic polyester having a melting point of at least 50° but below 100°C and a molecular weight not exceeding 10,000.

2. A composition according to claim 1 in which the polyester has a molecular weight from 500 to 2000. 10

3. A composition according to claim 1 or 2 in which the polyester has a melting point from 50° to 90°C.

4. A composition according to claim 1, 2 or 3 which also contains up to 100% by weight, based on the weight of the red phosphorus, of an oxide of copper, 15 zinc, silver, iron, antimony, vanadium, tin,, titanium, magnesium or cadmium.

5. A composition according to any one of claims 1 to 4 in which the phosphorus particles are coated with the polyester. 20

6. A composition according to any one of claims 1 to 5 in which the powder has a mean particle size not exceeding 200 μ.

7. A composition according to claim 1 substantially as hereinbefore described. - 12 .46179

8. A plastics composition which comprises a plastics material and from 0.2 to 20% by weight, based on the weight of the plastics material, of a flameproofing composition as claimed in any one of claims 1 to 7. 5

9. A composition according to claim 8 in the form of a shaped article.

10. A composition according to claim 8 substantially as hereinbefore described.