GB2262287A

GB2262287A - Flame-retardant filler for thermoplastic compositions

Info

Publication number: GB2262287A
Application number: GB9126300A
Authority: GB
Inventors: Bryan David Ludbrook
Original assignee: Evode Ltd
Current assignee: Evode Ltd
Priority date: 1991-12-11
Filing date: 1991-12-11
Publication date: 1993-06-16
Also published as: GB9126300D0

Abstract

A flame-retardant powdered filler for use in thermoplastic compositions comprises a mixture of powdered aluminium hydroxide at least the majority of which is in the alpha -trihydrate form and powdered hydrated basic magnesium/calcium carbonate. Preferably the powdered filler comprises from 25 to 80 per cent by weight of the powdered aluminium hydroxide and from 75 to 20 per cent by weight of powdered hydrated basic magnesium/calcium carbonate. The powdered filler may be incorporated in a thermoplastic polymeric base material such as ethylene vinyl acetate or ethylene co-octene to produce a flame-retardant thermoplastic composition containing about 60 per cent of the flame-retardant powdered filler.

Description

FLAME-RE@ARDANT FILLER FOR THERMOPLASTIC COMPOSITIONS Flame-@etardant thermoplastic compositions are known for use under conditions in which other thermoplastic compositions might constitute a fire haz@rd or be likely to fail by burning. Some flame-retardant thermoplastic compositions rely on the presence of halogen-containing components, but such components introduce new hazards in that they produce acrid toxic smoke if they catch fire.

Flame-retardant thermoplastic compositions which do not rely on h@logen-containing components have been produced by incorporating substantial proportions. typically about 60 per cent by weight, of powdered metal oxide, hydroxide and/or ca@benate filler or fillers in a thermoplastic resin matrix @ased on o@e@ni@ polymers. Metal hydroxides such as al@minium hydroxide prin@ipally in the α;-trihydrate form, commonly called alumina trihydrate, and magnesium hydroxide, calcium and magnesium carbonates and naturally occurring mine@ais such as @ol@mite, Huntite and Hydromagnesite have all been used in tais way. The spe@ification of Europe@n Patent application No. 0 393 813 Al des@@ibes a flame retardant comprising a mixture of 10 to 90% by weight of p@@der A an@ @@ to 10% by weight of powder B of magnesium hydroxide, the powder @ cont@ining 40 to @0% by weight of a powdered double salt of magnesium carbonste and ca@cium carbonate, preferably Huntite, and 60 to 30% @y @eight o@ powdere@ basic magnesium carbonate. 30 to 300 parts by weight o@ this flame retardant may be incorporated with 100 parts by weight of a thermop@astic resin to produce flame-retardant thermoplastic compositions, which may be used for cable sheathing or insulation, fire-arresting materials o@ wall materials.

The high levels, typically about. 60% by weight, of these metal oxide, hydroxide and carbonate fillers in thermoplastic compositions detract from the mechanical performance of the thermoplastic compositions as compared with similar compositions which are unfilled or contain lower proportions of filler.

The incorporation of coupling agents, such as silanes or carboxylic acids with long hydrocarbon tails together with small amounts of organic peroxides and co-agents such as multi-functional acrylates or methacrylates may be required to achieve a good balance of properties. Lubricants, antioxidants and pigments may also be needed to achieve specific requirements. These techniques anci technologies are well-known to persons involved in the torn,uiatíol-l of such compositions.

According to this invention a flame-retardant powdered filler for use in thermoplastic compositions comprises a mixture of powdered aluminium hydroxide at least the majority of which is in the a-trihydrate form and powdered hydrated basic magnesiumicalcium carbonate.

Preferably the powdered filler comprises from 25 to 80 per cent by weight of powdered aluminium hydroxide as specified above and from 75 to 20 per cent by weight of powdered hydrated basic magnesium/calcium carbonate.

Best results are obtained when the powdered filler comprises f'rom 50 to 75 per cent by weight of powdered aluminium hydroxide as specified above and from 50 to 25 per cent by weight of powdered hydrated basic msgnesium/calcil~In carbonate.

The invention includes a method of making flame-retardant thermoplastic compositions by incorporating the flame-retardant powdered filler in a thermoplastic polymeric base material and flame-retardant thermoplastic compositions containing the flame-retardant powdered filler. Suitable thermoplastic polymeric base materials are ethylene vinyl acetate ("EVA") and ethylene co-octene, but it is believed that any thermoplastic resin composition may be used.

Powdered aluminium hydroxide which is mainly in the a-trihydrate form, otherwise known as alumina trihydrate, as specified above is commercially available from various sources, for example under the Trade Mark TRIHYDE from Croxton & Gary or under the Trade Mark BACO from BA Chemicals Limited. It is known for use as a flame retardant. The powdered hydrated basic magnesium/calcium carbonate may be an intimate mixture of Huntite and Hydromagnesite in substantially equal proportions. This is a mineral occurring naturally in Greece and is marketed under the trade mark ULTRACARB by itlicrofine Minerals and Chemicals Limited. It is also known for use as a flame retardant.

rhe two tlame retardants mentioned have, when used in the same concentrations, broadly comparable oxygen indices. Since the effect of concentration on oxygen index is known to be approximately linear it would be expected that the oxygen index of a blend of the two would be the sum of the oxygen index contributions of the two components separately.The oxygen indices of compositions containing blends of the two would be expected to be the weighted arithmetic mean of the oxygen indices of equivalent compositions containing solely powdered aluminium hydroxide as specified above and solely powdered hydrated basic magnesium/calcium carbonate, provided that the overall concentration of flame retardant remained constant, the weighting factors being the relative proportions of the two flame retardants.

Surprisingly, we have found that the use of combinations of powdered aluminium um hydroxide and powdered hydrated basic magnesium/calcium carbonate as described produces oxygen indices (as defined in ASTM D2863) significantly greater than would be expected by simply adding the contributions of the two flame retardants in the proportions in which they are present in the compositions. In each, by mixing the two flame retardants together and incorporating them in a therrr,oplastic composition using an olefinic binder, there is obtained an oxygen index that is greater than would be expected in compositions containing the same total quantity of flame retardant but in which tlle flame retardant is either solely powdered aluminium hydroxide as specified above or solely powdered hydrated magnesium/calcium carbonate.

'i'he invention is illustrated by the examples listed in Tables 1 and 3.

Table 1 : Compositions based on ethylene-co-vinyl acetate binder.

EXAMPLE No. : @ 2 3 4 5 COMPONENT PARTS BY WEIGHT ELVAX 670 (EVA) 11.4 11.4 11.4 11.4 11.4 ELVAX 265 (EVA) 11.4 11.4 11.4 11.4 11.4 LEVAPREN 500 (EVA) 2.5 2.5 2.5 2.5 2.5 TRIHYDE OL1O7C (Aluminium hydroxide) 46.9 35.2 23.5 11.7 ULTRACARB CS (hydrated basic magnesium/calcium carbonate.) - 11.7 23.5 35.2 46.9 FLECTOL H @polymerized 1,2 dihydro-2,2,4-trimethylquindine - antioxidant) 0.05 0.05 0.05 0.05 0.05 UCARSIL DSC501 (silane, peroxide, acrylate and accelerator composition) 0.75 0.75 0.75 0.75 0.75 UCARSIL DSC502 (silane, peroxide, acrylate and accelerator -compositioni 0.75 v.75 0.75 0.75 0.75 CRODAMIDE SR (stearamide lubricant) 1.8 12.8 1.8 1.8 1.8 Samples were made according to each of these examples. Each was tested in accordance with American National Standard Specification ASTM D 2863 "Measuring the minimum oxygen concentration to support candle-like combustion of plastics (Oxygen index)". Comparative figures of the expected oxygen indices of the samples were calculated from data published by the producers of TRIHYDE uL107C and ULTRACARB CS. The results were as shown in Table 2.

Table 2. Comparison of Oxygen indices - Examples 1 to 5.

EXAMPLE No. : 1 2 3 4 5 Oxygen index (per cent) of samples with composition as in Table 1 35.3 39.3 39.5 37.4 36.5 Oxygen index of samples calculated from published data 35.3 35.6 35.9 36.2 36.5 Improvement in oxygen index by using TRIHYDE OL107C and ULTRACARB CS together 0.0 3.7 3.6 1.2 0.0 Percentage improvement 0.0 10.4 10,0 3.3 0.0 Table 3 : Compositions based on ethylene-co-octene binder.

EXAMPLE No. : 6 7 8 COtIPONEN'I' PARTS BY WEIGHT TEAMEX iOOOF (ECO) 34.7 34.7 34.7 EACO SF4E (Aluminium hydroxide) 60.2 30.1 ULTRACARS U45 (hydrated basic magnesium/ calcium carbonate) - 30.1 60.2 FLECTOL H (polymerized 1,2-dihydro-2,2,4 trimethylquindine - antioxidant) 0.07 0.07 0.07 Dicumyl peroxide (crosslinking and grafting agent) 0.04 0.04 0.04 Trimethylolpropane trimethacrylate (co-curative) 0.06 0.06 0.06 Silane A174 (Union Carbide) - coupling agent) 1.6 1.6 1.6 Dibutyl tin dilaurate (catalyst) 0.1 0.1 0.1 Again samples were made of each example and tests were made according to ASTM D 2863. Comparative figures of the expected oxygen indices were calculated from the producers' data. The results are shown in Table 4.

Table 4. Comparison of Oxygen indices - Examples 6 to 8.

EXAMPLE No. : 6 7 8 Oxygen index (per cent) of samples with composition as in Table 3 30.2 31.9 27.7 Oxygen index of samples calculated from published data 30.2 29.0 27.7 Improvement in oxygen index by using BACO SF4E and ULTRACARB U45 together 0.0 2.9 0.0 Percentage improvement 0.0 10.0 0.0 ELVAX is a Trade Mark of Du Pont (U.K.) Limited, FLECTOL is a Trade Mark of Monsanto Europe S.A., UCARSIL is a Trade Mark of Union Carbide Limited, CRODAMIDE is a Trade Mark of Croda Universal Limited and TEAMEX is a Trade Mark of DSM (U.K.) Limited.

Claims

1. A flame-retardant powdered filler for use in thermoplestic compositions comprising a mixture of powdered aluminium hydroxide at least the majority of which is in the a-trihydrate form and powdered hydrated basic niagnesiumcalcium carbonate.

2. A flame-retardant powdered filler as claimed in Claim 1 comprising from 25 to 80 per cent by weight of powdered aluminium hydroxide at least the majority of which is in the a-trihydrate form and from 75 to 20 per cent by weight of powdered hydrated basic magnesium/calcium carbonate.

A A lame-retardant powdered filler as claimed in Claim 1 comprising from 50 to 75 per. cent by weight of powdered aluminium hydroxide at least the majority ot which is in the a-trihydrate form and from 50 to 25 per cent by weight of powdered hydrated basic magnesium/calcium carbonate.

4. A @lame-retardant powdered filler substantially as hereinbefore described with reference to any of Examples 1 to 8.

5. A method of making a flame-retardant thermoplastic composition comprising incorporating a flame-retardant powdered filler as claimed in any ot Claims 1 to 4 in a thermoplastic polymeric base material so that the iller comprises about 60 per cent of the composition.

6. A method as claimed in Claim 6 wherein the thermoplastic polymeric base material is ethylene vinyl acetate or ethylene-co-octene.

7. A tlarrle-retardent thermoplastic composition comprising a thermoplastic polymeric base material wherein is dispersed a flame-retardant powdered filler as claimed in any of Claims 1 to 4, the filler comprising about 60 per cent by weight of the composition.

8. A method of making a flame-retardant thermoplastic composition substantially as hereinbefore described.

9. A flame-retardant thermoplastic composition substantially as hereinbefore described with reference to any one of Examples 1 to 8.