GB2267497A - Polyamide moulding composition - Google Patents

Abstract

A polyamide moulding composition contains a thermoplastic polyamide, such as nylon 6 or nylon 66. together with red phosphorus and finely divided calcium carbonate, optionally with glass fibres, in which the amount of glass fibres and calcium carbonate fall within the ratio:- x + y </= 50 where x is the percentage weight of calcium carbonate in the composition and y is the percentage by weight of glass fibre, where x >/= 5 and y is 0-45. Additionally 1-30% by weight of an olefin copolymer (eg. ethylene/vinyl acetate copolymer) is also included.

Description

Improvements in or relating to polyamide compositions This invention relates to polyamide compositions, and more particularly to such compositions which contain flame retardants.

In moulding compositions of polyamides such as nylon 6 and nylon 66 flame retardants are widely used materials. Red phosphorus may be used as a flame retardant in such compositions and its use in various compositions has been proposed. For example in published European Patent Application 0,303,031 Al a polyamide moulding composition is proposed in which red phosphorus is used as a flame retardant and an olefin polymer of a specificed type is also present as an additive to improve the flame resistance.The definition of the olefin polymer in this patent embraces a wide range of compounds which include copolymers containing units derived from a primary or secondary C1-C12 alkyl ester of acrylic or methacrylic acid or mixtures of such esters and/or units derived from an acid functional and/or latent acid functional monomer of an ethylene-unsaturated mono- or di- carboxylic acid.

Published UK Patent Application No 2,200,913A discloses a polyamide moulding composition with reinforcing mineral fibres which contains 4 to 15% red phosphorus and 5 to 40% magnesium hydroxide for flame retardancy with good electrical tracking resistance, the total of both being not more than 50 per cent by weight of the composition and their amounts being such that 3P + M ? 20 where P is per cent by weight of red phosphorus and M is per cent by weight of magnesium hydroxide.

Published UK Patent Application No 2,200,914A discloses a moulding composition based on a thermoplastic polyamide which contains 5 to 15% red phosphorus and 5 to 50% magnesium carbonate for flame retardancy with a good electrical tracking resistance, their combined total being not more than 55 per cent by weight of the composition and their amounts being such that 3P + C > , 30 where P is per cent by weight red phosphorus and C is per cent by weight magnesium carbonate in the total composition. The composition can also include reinforcing fibres.

Whilst the magnesium hydroxide and magnesium carbonate have beneficial properties in the compositions disclosed in these published applications they do give rise to processing difficulties during compounding of the compositions containing them.

We have now found that the addition of precipitated calcium carbonate improves the heat resistance and improves the tracking resistance in polyamides flame retarded with red phosphorus.

According to the present invention a polyamide moulding composition comprises a thermoplastic polyamide, red phosphorus and finely divided calcium carbonate.

The thermoplastic polyamide is preferably an injection mouldable polymer with a melting point above 1800C, for example, nylon 6 or nylon 66.

As flame retardant red phosphorus is an essential ingredient of the polyamide composition but the red phosphorus is preferably treated in order to reduce its handling difficulties, since red phosphorus alone can be very dangerous in handling. Thus the red phosphorus may be carried on a polymeric carrier, and/or may be encapsulated with a suitable substance such as a polymer or resin.

Preferably the amount of red phosphorus in the composition is 1 to 15 per cent by weight of the total composition.

Finely divided calcium carbonate is used in this invention, and may be synthetic or the more usual naturally occurring forms of calcium carbonate. A preferred grade of precipitated calcium carbonate has acicular shaped fine particles ie is in the oragonite form rather than calcite, for ease of processing.

The amount of calcium carbonate used in the moulding composition will depend upon whether the composition is glass fibre reinforced.

Glass fibre reinforcement is an optional ingredient of the composition and if X is the percentage by weight of calcium carbonate in the composition and Y is the percentage by weight of glass fibre X + Y 4 50 where X 5 and Y is 0 to 45 The presence of the calcium carbonate in the composition has two beneficial effects, both of which are surprising, in that mouldings made from the compositions with the calcium carbonate have increased Izod impact strength (whereas a lowering of this would be expected) and improved retention of impact strength during ageing, and furthermore the mouldings have improved electrical tracking resistance.

The precipitated calcium carbonate does not have such good beneficial effects as magnesium hydroxide, but the difference is not acute and the calcium carbonate is both much cheaper and free from processing difficulties.

A further optional ingredient of the composition is an olefin copolymer, which could be of the kind described in the EP 0,303,031 mentioned above. Preferably, however, the olefin copolymer is a copolymer from ethylene and an unsaturated ester of a saturated C1 to C4 carboxylic acid.

In said preferred copolymer the proportion of said unsaturated ester may be in the range 5% by weight up to 50% by weight, and preferably said ester is a vinyl ester, more preferably vinyl acetate.

Optionally the preferred olefin copolymer may also be grafted with units containing groups which are reactive in relation to thermoplastic polyamides, for example it may be grafted with units derived from acrylic acid, or maleic anhydride or an epoxy compound such as glycidyl methacrylate.

Preferably the polymer component of the polyamide composition contains 1 to 30% by weight of the olefin copolymer.

If desired other ingredients may also be added to the compositions of this invention, such as pigments, stabilisers, lubricants, mineral fillers etc, as is usual in a moulding composition.

The invention will now be described in more detail by means of examples.

EXAMPLES Flammability Testing The method used was the standard Underwriters Laboratories test method UL94. VO means that the specimens burnt for less than lOs after removal of flame, that the total burn time for ten applications of the flame on five specimens was less than 50 seconds. In addition no flaming drops are permitted. In V1 classification no specimen burns for longer than 30 seconds after the application of the flame and the total burning time for 10 specimens is less than 250 seconds. No flaming drops are permitted. The same criteria apply in V2 classification except that some flaming drops are permitted.

In addition to these classifications, the average burning time for each application of flame was calculated and the occurrence of non-flaming drops was noted (10 specimens).

Electrical Tracking Resistance Testing The test equipment used is that of the Comparative Tracking Index test of the European Standard IEC 112 (DIN 53480). An aqueous solution containing 0.1% NH4C1 and 0.5% surfactant (Nansa HS 85/S ex Albright and Wilson) was dropped at 30 second intervals on to the surface of the mouldings between two electrodes carrying the applied voltage. Platinum electrodes were used, with trips at 0.5 amps and 2 secs.

Results are expressed in the tables below for each applied voltage as "failures", or "passes" at 50 drops total.

Examples 1 and 2 Two compositions of nylon 66 were prepared with and without precipitated calcium carbonate for comparison.

The compositions were made by first blending the ingredients shown in Table I, and then fully compounded in a Baker Perkins twin-screw extruder.

TABLE I Ingredient Example 1 Example 2 Nylon 66 44 55 Coated Red Phosphorus 7.1 7.1 Ethylene/Vinyl Acetate Copolymer 3 3 Carbon Black Masterbatch N54 3 3 Nylon 6 7 7 Glass Fibre 25 25 Lubricant Wax 0.9 0.9 Precipitated Calcium Carbonate 10 0 In each example the red phosphorus used (MASTERFLAM P70S) was encapsulated in a polyamide carrier (70% by weight of red phosphorus). The precipitated calcium carbonate used was grade 40-M60 of Mississipi Lime Company and the glass fibres were grade 429YZ from Owens Corning Fibreglass, chop length 4.5mm. The ethylene/vinyl acetate copolymer used was LACQTENE V grade 8458 commercially available from Atochem Limited, and the lubricant was was LOTADUR WAX HC 8571. The carbon black was masterbatched in nylon 6 and was used only as a pigment.

Sample mouldings were made by injection moulding from each composition on a standard BIPEL 60/26 machine using a barrel temperature of 270 C.

These were tested for impact strength using the IZOD impact test, for flammability and for Electrical Tracking Resistance. The results of these tests are given below in Table II.

TABLE II Test Example 1 Example 2 IZOD Unnotched Impact (J/M) Unaged 1092 912 Aged at 195 0C for 24 hrs 425 257 % retention 39 28 Flammability - UL94 at 1.5mm Class VO VO Average Burn Time 0.1 0.1 % Edge Burns 0 10 Electrical Tracking Resistance At 500V 5 passes Not tested At 450V Not tested 3 Fails At 400V Not tested 5 Passes Examples 3 to 6 Four compositions of nylon 66 were prepared, three with differing grades of calcium carbonate and one without calcium carbonate for comparison.

The compositions were made following the same procedures as Examples 1 and 2 using the ingredients shown in parts by weight in TABLE III below.

TABLE III Example No Ingredient 3 4 5 6 Nylon 66 57.8 57.8 57.8 67.8 Coated Red Phosphorus 7.2 7.2 7.2 7.2 Glass Fibre 25 25 25 25 Acicular precipitated CaCO3 (oragonite) 10 - Precipitated CaC03 (calcite) - 10 Natural CaCO3 (calcite) - - 10 - The coated red phosphorus was the same grade as used in Examples 1 and 2, and the glass fibre was R23D grade glass fibre from Owens Corning Fibre Glass.

The acicular calcium carbonate was grade 40-M60 as in Examples 1 and 2. The other precipitated (calcite) calcium carbonate was CALOFORT S and the natural (calcite) calcium carbonate was SNOWCAL 70 (ex Croxton & Cary).

Sample mouldings were made by injection moulding from each composition as before and tested for electrical tracking resistance, unnotched Izod impact strength and flammability.

The results of these tests are given below in TABLE IV.

TABLE IV Example No Test 3 4 5 6 Electrical Tracking Resistance 550V F F F F 500V P P P F 450V P P P P Izod unnotched impact strength j/m 550 680 658 580 Flammability - UL94 at 1.5mm Class VO VO VO V1 From these tests it can be seen that all the grades of calcium carbonate improved the electrical tracking resistance of the formulation and the calcite grades appeared to be more effective in improving impact resistance.

It will be noted that the formulations in Examples 3 to 6 do not contain Ethylene/Vinyl Acetate copolymer and have markedly inferior impact resistance to the formulations in Examples 1 and 2.

Claims (9)

1. A polyamide moulding composition which comprises a thermoplastic polyamide, red phosphorus and finely divided calcium carbonate.

2. A polyamide moulding composition according to claim 1 in which the amount of red phosphorus is 1 to 15 per cent by weight of the composition.

3. A polyamide moulding composition according to claim 1 or 2 which optionally includes glass fibres, in which the amounts of calcium carbonate and glass fibres fall within the following relationship X + Y 4 50 X being the percentage weight of calcium carbonate in the composition Y being the percentage by weight of glass fibre in the composition where X ? 5 and Y is in the range O to 45.

4. A polyamide moulding composition according to any one of claims 1 to 3 which also includes an olefin copolymer in an amount such that the polymer component of the polyamide composition contains 1 to 30 per cent by weight of the olefin copolymer.

5. A polymer moulding composition according to claim 4 in which the olefin copolymer is a copolymer from ethylene and an unsaturated ester of a saturated C to C4 carboxylic acid.

6. A polyamide moulding composition according to claim 5 in which the proportion of said unsaturated ester in the olefin copolymer is in the range 5% by weight up to 50% by weight.

7. A polyamide moulding composition according to claim 5 or 6 in which said olefin copolymer is an ethylene/ vinyl acetate copolymer.

8. A polyamide moulding composition substantially as described herein in Example 1.

9. A polyamide moulding composition substantially as described herein in Example 3, 4 or 5.