GB2288808A

GB2288808A - Moulding compositions containing a polyamide

Info

Publication number: GB2288808A
Application number: GB9407686A
Authority: GB
Inventors: Richard Scott Barnes; Richard Stuart Williams
Original assignee: T&N Technology Ltd
Current assignee: Federal Mogul Technology Ltd
Priority date: 1994-04-19
Filing date: 1994-04-19
Publication date: 1995-11-01
Also published as: WO1995028439A1; GB9407686D0

Abstract

A moulding composition contains a polyamide, eg nylon 6 or nylon 66, and, optionally, a filler, such as magnesium hydroxide which acts as a flame-retardant. In order to reduce surface defects in the moulding, the composition also contains phthalimide.

Description

MOVLDING COMPO < ITIONS CONTAINING A POLYAMIDE This invention is concerned with moulding compositions which contain a polyamide, e.g. nylon 6 or nylon 66, and is especially concerned with such compositions which contain a filler, eg magnesium hydroxide as a flame retardant.

Polyamides, such as nylons, are widely used for moulding components and, for some moulding applications, are mixed with a flame-retardant so that the moulded component exhibits flame retardant characteristics. Such applications include electrical lamp-holders, and switch housings.

Magnesium hydroxide is a flame retardant which has been suggested for use with nylon. This material, when subjected to a flame, decomposes endothermically with the liberation of water. Nylon containing magnesium hydroxide has, however, been found to be difficult to mould because of its high melt viscosity and, furthermore, it is found that the mouldings have obvious surface defects which render them unacceptable commercially. Such surface defects manifest themselves by the appearance of white patches on the surface of the moulding. Various attempts have been made to overcome this problem but without achieving complete success. The most successful previous attempt known to the applicants involves the addition of organic sulphonamide to the moulding composition (see GB 2,237,573A) but even this has not achieved total success.

It is an object of the present invention to provide a moulding composition containing a polyamide which produces mouldings which are substantially free of surface defects of the type referred to.

It is a further object of the invention to provide a moulding composition containing a polyamide and magnesium hydroxide which'produces mouldings which are substantially free of surface defects of the type referred to.

The invention provides a moulding composition containing a polyamide wherein the composition also contains phthalimide.

Phthalimide is recorded in the Chemical Abstract Service Registry under number CAS 85-41-6.

A moulding composition according to the invention is found to produce mouldings with reduced surface defects.

The composition is also found to be easier to mould making it possible to mould compositions with higher concentrations of fillers.

Preferably, the phthaimide provides 0.1 to 5 per cent by weight of the composition, eg 0.5 to 5 per cent. In some compositions, about 1 per cent of phthalimide is found to result in saleable mouldings, ie with an acceptable level of surface detects, and 2.5 per cent was found to result in substantially no discernable surface defects.

The polyamide may be nylon 6, nylon 66, nylon 6.12, nylon 6.10 or another suitable polyamide. The polyamide may also be a co-polymer of two forms of nylon, eg nylon 6 and nylon 66.

The composition may also comprise a filler, eg flameretardant such as magnesium hydroxide which may be present in 45 to 65 per cent by weight of the composition, or if a lower standard of flame-retardancy is acceptable, the percentage may be 20 to 45. The composition may contain additional fillers, for example, a ferromagnetic material such as strontium ferrite. The composition may also contain reinforcing fibres, e.g. glass fibres, which may be present in up to 35% by weight depending on the amount of magnesium hydroxide or other filler which is present. A plasticiser may also be used, eg butyl benzene sulphonamide which may be present in amounts of approximately 1.25 per cent by weight.

There now follow detailed descriptions of two moulding compositions which are illustrative of the invention.

The first illustrative moulding composition was a formulation of 40 parts nylon 6, 60 parts magnesium hydroxide (Magnifin H5), 0.3 parts calcium stearate (as a mould lubricant), 1 part phthalimide, and 25 parts glass fibre (all parts by weight). The composition was injection moulded into test discs which were subjected to tests in comparison with a comparison composition of the same formulation but with the phthalimide omitted.

The discs made from the comparison composition had very noticeable surface defects in the form of white marks covering the surface. It was considered that mouldings made from the comparison composition would have been unsaleable as their appearance would have been unacceptable to a customer. The discs moulded from the first illustrative composition had noticeable surface defects but these were far less marked than in the comparison composition. It was considered that mouldings made from the first illustrative composition would have been acceptable to customers.

In a flammability test, the discs made from the comparison composition gave a mean burn time of 3.6 seconds which is within acceptable limits. A tensile strength test gave an average value of 120NPa, an elongation at break test gave a value of 1.1%. A flexural strength test gave a value of 192NPa. These tests were repeated using the discs made from the first illustrative composition. The mean burn time was 4.7 seconds (also acceptable), the tensile strength was 126spa, the elongation at break was 1.0%, and the flexural strength was 192spa. Thus, in all the tests, the first illustrative composition substantially equalled the comparison composition. The first illustrative composition was also easier to mould.

The second illustrative composition was the same as the first except that 2.5 parts by weight of phthalimide and 70 parts by weight of magnesium hydroxide were included. Discs injection moulded from the second illustrative composition were found to have no discernable surface defects in the form of white marks. The abovementioned tests were repeated for the second illustrative composition. The mean burn time was measured as 1.5 seconds, the tensile strength as 121MPa, the elongation at break as 1.3%, and the flexural strength as 191spa.

The first and the second illustrative compositions were both easier to mould, ie required less injection force, than the comparison composition.

Claims

1 A moulding composition containing a polyamide wherein the composition also contains phthalimide.

2 A moulding composition according to Claim 1, wherein the phthalimide comprises 0.1 to 5 per cent by weight of the composition.

3 A moulding composition according to either one of claims 1 and 2, wherein the polyamide is nylon 6.

4 A moulding composition according to either one of claims 1 and 2, wherein the polyamide is nylon 66.

5 A moulding composition according to any one of Claims

1 to 4, wherein the composition also comprises a filler.

6 A moulding composition according to claim 5, wherein filler is magnesium hydroxide.

7 A moulding composition according to any one of claims

1 to 4, wherein the composition also comprises a ferromagnetic material.

8 A moulding composition according to any one of Claims

1 to 7, wherein the composition also contains reinforcing fibres.

9 A moulding composition substantially as hereinbefore described with reference to the first illustrative composition or the second illustrative composition.

10 A component moulded from a moulding composition according to any one of claims 1 to 9.