Polyamide composition having high thermal conductivity

Abstract

The present invention relates to a composition based on a polyamide matrix having a high thermal conductivity and comprising specific proportions of alumina and of graphite and also a flame-retardant system. This composition may in particular be used for producing components for lighting devices comprising light-emitting diodes.

Claims

1. A composition comprising: a) a polyamide matrix; b) from 2% to 30% by weight of alumina; c) from 15% to 50% by weight of a natural or artificial graphite having a particle size of from 0.1 to 100 m; and d) from 5% to 40% by weight of a flame-retardant system; wherein the percentages by weight are expressed with respect to the total weight of the composition.

2. The composition as claimed in claim 1, wherein the composition comprises from 20% to 80% by weight of polyamide, with respect to the total weight of the composition.

3. The composition of claim 1, wherein the composition comprises from 2% to 20% by weight of alumina.

4. The composition of claim 1, wherein the composition comprises from 20% to 40% by weight of graphite.

5. The composition of claim 1, wherein the flame-retardant system comprises at least one flame retardant selected from the group consisting of: phosphorus-comprising flame retardants, flame retardants of nitrogen-comprising organic compound type and flame retardants comprising halogenated derivatives.

6. The composition of claim 1, wherein the flame-retardant system comprises at least one phosphonic acid or its salt or one phosphinic acid or its salt.

7. The composition of claim 1, wherein the composition further comprises reinforcing or bulking fillers.

8. The composition of claim 1, wherein the composition comprises: from 2% to 15% by weight of the alumina; from 20% to 35% by weight of the graphite; and from 5% to 20% by weight of the flame-retardant system.

9. The composition of claim 1, wherein the composition exhibits a thermal conductivity of from greater than 0.1 W/mK to 3.0 W/mK.

10. The composition of claim 1, wherein the composition exhibits a thermal conductivity of 3.0 W/mK.

Description

EXPERIMENTAL PART

Example 1

Preparation of the Compositions

(1) Compounds used: Polyamide 6.6 with a relative viscosity of 2.7 (according to the standard ISO 307, using sulfuric acid as solvent), sold by Rhodia Engineering Plastics under the name Technyl 27 A00. Masterbatch: 20% by weight phenol-formaldehyde/80% by weight graphite Alumina (aluminum oxide) KAM OCV 983 Glass fiber from Owens Corning Vetrotex Flame-retardant system: Exolit OP1230 from Clariant and melamine polyphosphate Melapur 200 Formulation additives: heat stabilizers and lubricants. 0.2% by weight in all the formulations.

(2) In order to manufacture compositions comprising varied proportions of additives and filler, the polyamide and the various additives are blended by extrusion, via a twin-screw extruder (barrel temperature: 250-290 C., flow rate: 30 kg/h, rotation: 250 rpm). The final compositions are then extruded and granulated, and then injection molded. The results are given in table 1.

(3) TABLE-US-00001 TABLE 1 Composition C1 C2 C3 C4 1 2 PA 6.6 84.3 39.9 65.9 31.9 35.9 45.3 Graphite MB 30.0 30.0 30.0 Alumina 4.0 38.0 4.0 9.0 GF 5.0 5.0 5.0 5.0 5.0 5.0 Exolit 7 16.6 16.6 16.6 16.6 7 MPP 3.5 8.3 8.3 8.3 8.3 3.5 Surface resistivity 15 6 15 15 8 9 (log ohm square) Thermal conductivity 0.1 1.5 0.5 1.0 3.0 3.0 (W/mK) UL 94 @ 0.8 mm V2 V0 V0 V0 V0 V1 Ultimate bending 1390 830 1170 830 980 1020 strength (kgf/cm.sup.2) Flexural modulus 45 000 42 300 69 000 (kgf/cm.sup.2) Izod impact 6.4 t (kgf 3.8 2.0 3.0 1.0 1.8 2.5 cm/cm) HDT (18.5 kgf/cm.sup.2) 230 208 202 208 201 215 The proportions are expressed as percentage by weight, with respect to the total weight of the composition

(4) The measurements were carried out with the following standards: Izod impact strength according to the standard ASTM D-256 Ultimate bending strength and flexural modulus according to the standard ASTM D638 Surface resistivity according to the standard ASTM D257 (Standard Test Methods for DC Resistance or Conductance of Insulating Materials) Thermal conductivity according to the standard ASTM E1461 (Standard Test Method for Thermal Diffusivity by the Flash Method)

(5) It is thus observed that the combination according to the invention of high proportions of graphite and of low proportions of alumina in the polyamide composition makes it possible to obtain a unique compromise in mechanical, resistivity to electrical current and thermal conductivity properties which renders this composition suitable for the manufacture of articles for applications related to semiconductors or light-emitting diodes.