GB2107721A

GB2107721A - Improvements in stabilisers for vinyl resins

Info

Publication number: GB2107721A
Application number: GB08228396A
Authority: GB
Inventors: Derek Gordon Pearson
Original assignee: Associated Lead Manufacturers Ltd
Current assignee: Associated Lead Manufacturers Ltd
Priority date: 1981-10-23
Filing date: 1982-10-05
Publication date: 1983-05-05
Also published as: GB2107721B

Abstract

The fire hazard attending the use of dibasic lead phosphite as a stabiliser for vinyl resins is reduced by mixing with the dibasic lead phosphite an additive selected from hydroxides or hydrated oxides of aluminium, magnesium or antimony, stearates of barium or calcium, dibasic lead stearate and carbonates of calcium or magnesium.

Description

SPECIFICATION Improvements in stabilisers for vinyl resins Dibasic lead phosphite has the formula 2Pb0 PbH PO3 21 H20 and is used as a stabiliser for vinyl resins, e.g. polyvinyl chloride (P.V.C.) against weathering, i.e. it provides protection against U.V.

radiation and mild thermal excitation. Stabilisation is achieved by the presence of both basic lead and phosphite groups (anti-oxidant) on the molecule.

Unfortunately the presence of both groups causes the material to be heat sensitive and two exothermic reactions occur: (i) 2Pb0 PbH P03 H PbO PbH P04 + Pb.

(ii) 2Pb + 2 (atmosphere) e 2Pb0.

As can be seen reaction (i) does not require atmospheric oxygen and in practice once ignition occurs, a fire is difficult to extinguish. Inert atmospheres have been used in an attempt to achieve this.

While this appears to have extinguished the fire, on re-exposure to air the strongly exothermic reaction (ii) re-generates the fire. The only known method of effectively extinguishing a dibasic lead phosphite fire is to reduce the temperature to below the initiation temperature of reaction (i) and this is achieved by dowsing the fire with water. Dibasic lead phosphite is usually coated with a water repellant coating, to aid its dispersibility into P.V.C. and to prevent reactions with atmospheric carbon dioxide and moisture on storage, and this renders it difficult to wet the burning powder with water. Fires have been reported during manufacture, during storage and on a lorry carrying dibasic lead phosphite following a road accident.

Because of the fire hazard, dibasic lead phosphite powder is classified under 4:1 inflammable solids according to the Department of Trade and Industry and is required to be packed in 'effectively closed' packages. This in the United Kingdom means package in metal drums which are costly. In addition a test method and classification is being considered by the United Nations Secretariat Committee of experts on the Transport of Dangerous Goods.

The ignition temperature for reaction (i) is difficult to quantify as the temperature is dependent on tirne and weight. For instance a sample can ignite after five hours at 3000C and fail to ignite after 10 seconds at 4000C and a small sample can ignite and self-extinguish from a burning cigarette whereas a large sample can burn vigorously under the same conditions.

Consequently two tests have been used to assess the fire hazard, a hot surface applied to the powder (ignition temperature) and the rate of burning once ignition has started (propagation test). This latter test is particularly relevant to storage in the hold of a ship as slow burning rates can allow fire fighting equipment to be brought to the scene of the fire. The U.K. classification allows a maximum burning rate of 66 mm/min. and the proposed U.N. classification allows a maximum of 100 mm/min.

This latter classification is considered by some experts to be too high and it may be reduced to the U.K.

limit.

The above tests are as follows:- PROPAGATION TEST A 20 x 10 mm. cross section x 250 mm. length pile of powder is made using a metal former. The former is removed and the powder ignited at one end by means of an incandescent wire. When the fire has progressed 50 mm., the time for a further 100 mm. is taken and the rate is calculated.

IGNITION TEMPERATURE A 2 mm. thick thermocouple probe is heated in a flame to a temperature in excess of the test temperature. As the probe cools to the test temperature the probe is applied to a 10 gram heap of powder for 1 5 seconds. If ignition occurs the test is carried out on a fresh sample at a lower temperature. If ignition does not occur the powder is re-tested at a higher temperature. The result is taken when the ignition occurs at a temperature 100C above that at which ignition does not occur.

The present invention is based on the discovery that by addition to the dibasic lead phosphite powder of certain materials which are compatible with P.V.C., the temperature of a phosphite fire can be so reduced that the fire self-extinguishes or burns at a slow rate.

It provides a stabiliser for vinyl resins which consists of a mixture of dibasic lead phosphite and an additive selected from hydroxides or hydrated oxides of aluminium, magnesium or antimony, stearates of barium or calcium, dibasic lead stearate and carbonates of calcium or magnesium, the additive being present in an amount sufficient to give a fire propagation rate not exceeding 100 mm/min.

The mixture can be formed by coprecipitation with the dibasic lead phosphite during course of manufacture or by blending the additive with the dibasic lead phosphite powder.

Such a mixture can be shipped in bags and is less subject to fires during handling and storage than dibasic lead phosphite containing no such additives. The mechanism of the invention is based on the fact that the additives have strong or weak endothermic reactions occurring above 1 200C and below 4500C which counteract the exothermic reaction (1).

EXAMPLES (i) Coprecipitate Formation 219 gms. of litharge are mixed with 1500 ccs. of water at 600C. 1.2 gms. of acetic acid catalyst are added and 27 gms. of phosphorous acid dissolved in 50 ccs. of water are added over a period of 30 minutes. The resulting white slurry is stirred for 1 5 minutes and the required amount of additive is added to the slurry (12 gms. for 5% addition). 1 gm. of stearic acid is dissolved in 3 gms. of dioctyl phthalate plasticiser and the liquid is added to the slurry. The treated solids are filtered and dried at 1 000C and then ground to a fine powder.

(ii) Mixture formation A coated dibasic lead phosphite powder is prepared without additives as above and blended in a laboratory mixer with the required amount of powdered additive.

The coprecipitates and mixtures were assessed for fire risk according to the table below in which M denotes a mixture and C a coprecipitate:- Additive (Coprecipitate Fire Propagation Ignition Example or mixture) Rate Temperature 1. None - mm/min. 500''C 2. 10% Aluminium Hydroxide M Nil above 900 C 7% Aluminium Hydroxide M Self-extinguished 600 C 5% Aluminium Hydroxide M 23 mm/min. 550 C 2% Aluminium Hydroxide M 50 mm/min. 530 C 3. 1 596 Aluminium Hydroxide C Nil above 900C 10% Aluminium Hydroxide C 15 mm/min, 600'C 5% Aluminium Hydroxide C 35 mm/min. 5500C 2% Aluminium Hydroxide C 58 mm/min. 500Cc 4. 10% Magnesium Hydroxide M Nil above 900 C 5% Magnesium Hydroxide M Nil above D00 C 2% Magnesium Hydroxide M 38 mm/min. 600 C 5. 10% Magnesium Hydroxide C Nil above 900?e 5% Magnesium Hydroxide C 30 mm/min. 600 C 2% Magnesium Hydroxide C 45 mm/min. 600 C 6. 40% Calcium Stearate M 5 mm/min. 800 C 25% Calcium Stearate M 14 mm/min. 500 C 10% Calcium Stearate M 40 mm/min. 5000C 5% Calcium Stearate M 58 mmímin. 500 C 7. 30% Calcium Stearate C Nil above 900 C 20% Calcium Stearate C 14 mmimin. 550 C 1096 Calcium Stearate C 50 mm/min. 500 C Additive (Coprecipitate Fire Propagation Ignition Example or mixture) Rate Temperature 8. 30% Calcium Carbonate M 18 mm/min. 5500C 30% Calcium Carbonate C 18 mm/min. 5500C 20% Calcium Carbonate M 30 mm/min. 550 C 10% Calcium Carbonate M 38 mm/min. 550 C 9. 15'S0 Dibasic Lead Stearate M 15 mm/min. 5500C 15% Dibasic Lead Stearate C 15 mm/min. 5500C 10% Dibasic Lead Stearate M 50 mm/min. 550 C 5% Dibasic Lead Stearate M 71 mm/min. 5500C 10. 259/0 Hydrated Antimony Pentoxide M 15 mm/min. 7000C 25% Hydrated Antimony Pentoxide C 15 mm/min. 7000C 20% Hydrated Antimony Pentoxide M 25 mm/min. 550 C 5% Hydrated Antimony Pentoxide M 40 mm/min. 5500C 2% Hydrated Antimony Pentoxide M 62 mm/min. 500 C 11. 20% Barium Stearate M 4 mm/min. 6000C 20% Barium Stearate C 8 mm/min. 600 C 10% Barium Stearate M 10 mm/min. 5000C 5% Barium Stearate M 20 mm/min. 5000C 2% Barium Stearate M 63 mm/min. 5000C 12. 20% Magnesium Carbonate M Nil above 900 C 20% Magnesium Carbonate C Nil above 900 C 1096 Magnesium Carbonate M Self-extinguished 800 C 5% Magnesium Carbonate M 10 mm/min. 5000C 2% Magnesium Carbonate M 43 mm/min. 5000C

Claims

1. A stabiliser for vinyl resins which consists of a mixture of dibasic lead phosphite and an additive selected from hydroxides or hydrated oxides of aluminium, magnesium or antimony, stearates of barium or calcium, dibasic lead stearate and carbonates of calcium or magnesium, the additive being present in an amount sufficient to give a fire propagation rate not exceeding 100 mm/min.

2. A stabiliser according to claim 1, which is a physical mixture of dibasic lead phosphite powder and the additive.

3. A stabiliser according to claim 1, which is a coprecipitate of dibasic lead phosphite and the additive.

4. A stabiliser according to claim 1, in which the additive is 2-1 5% by weight of aluminium hydroxide.

5. A stabiliser according to clairn 1, in which the additive is 2-10% Ouzoby weight of magnesium hydroxide.

6. A stabiliser according to claim 1, in which the additive is 540% by weight of calcium stearate.

7. A stabiliser according to claim 1, in which the additive is 1030% by weight of calcium carbonate.

8. A stabiliser according to claim 1, in which the additive is 5-1 5% by weight of dibasic lead stearate.

9. A stabiliser according to claim 1, in which the additive is 225% by weight of hydrated antimony pentoxide.

10. A stabiliser according to claim 1, in which the additive is 2-20% by weight of barium stearate.

11. A stabiliser according to claim 1, in which the additive is 2-20% by weight of magnesium carbonate.

New claims or amendments to claims filed on 25 January 1983.

Superseded claims 1.

New or amended claims:

1. A stabiliser for incorporation in vinyl resins which consists primarily of dibasic lead phosphite, is capable of storage with reduced fire hazard and is a mixture of dibasic lead phosphite and an additive selected from hydroxides or hydrated oxides of aluminium, magnesium or antimony, stearates of barium or calcium, dibasic lead stearate and carbonates of calcium or magnesium, the additive being present in an amount sufficient to give a fire propagation rate not exceeding 100 mm/min.