FLAME-RETARDANT POLYAMIDE COMPOSITIONS

Abstract

The present invention relates to polyamide-based compositions comprising at least one filler from the group consisting of aluminum oxide, boron nitride and triclinic aluminum silicate and also the use of these compositions for producing products having relatively high flame resistance requirements, particularly preferably products having relatively high glow wire requirements, in particular components for electric current- and voltage-conducting components in domestic appliances.

Claims

1. A composition comprising: a) 20 to 90% by weight of at least one polyamide; and b) 10 to 80% by weight of at least one electrically insulating, thermally conductive filler selected from the group consisting of b1) aluminum oxide, where the sum total of all the percentages by weight is always 100.

2. The composition as claimed in claim 1, wherein the component b1) is in the form of fine needles, platelets, spheres, or irregularly shaped particles.

3. The composition as claimed in claim 2, wherein the particle sizes of the component b1) is are 0.1 to 300 m.

4. The composition as claimed in claim 2, wherein the thermal conductivity of the component b1) is 10 to 400 W/mK.

5. (canceled)

6. (canceled)

7. (canceled)

8. The composition as claimed in claim 1, further comprising: c) 5 to 70% by weight, based on the total composition, of glass fibers, where the amounts of the other components are reduced to such an extent that the sum of all the percentages by weight is always 100.

9. The composition as claimed in claim 8, wherein the glass fibers are provided with a size system or a bonding agent, or bonding agent system, particularly preferably one based on silane.

10. The composition as claimed in claim 8, further comprising: d) 0.01 to 3% by weight, based on the total composition, of at least one thermal stabilizer, where the amounts of the other components are reduced to such an extent that the sum of all percentages by weight is always 100.

11. The composition as claimed in claim 10, wherein the thermal stabilizer is selected from the group consisting of sterically hindered phenols, which are compounds which have a phenolic structure and have at least one bulky group on the phenolic ring, preferably sterically hindered phenols of the formula (II), ##STR00007## where R.sup.1 and R.sup.2 are each an alkyl group, a substituted alkyl group or a substituted triazole group, where the radicals R.sup.1 and R.sup.2 can be identical or different, and R.sup.3 is an alkyl group, a substituted alkyl group, an alkoxy group or a substituted amino group.

12. The composition as claimed in claim 1, further comprising at least one of: c) 5 to 70% by weight, based on the total composition, of glass fibers, d) 0.01 to 3% by weight, based on the total composition, of at least one thermal stabilizer, and e) 1 to 40% by weight, based on the total composition, of at least one flame retardant, where the amounts of the other components are reduced to such an extent that the sum of all percentages by weight is always 100, preferably organic halogen compounds with synergists or organic nitrogen compounds or organic/inorganic phosphorus compounds, which are used individually or in admixture with one another.

13. A process for producing a composition as claimed in claim 1, the process comprising mixing the components a) and b) with one another in a mixing apparatus.

14. The process as claimed in claim 13, further comprising mixing of the components in a melt at a temperature of 240 to 300 C.

15. The process as claimed in claim 14, the wherein the mixing is carried out in an extruder, and the process further comprises discharging the mixture as strand through at least one extruder outlet, cooling the strand until it is pelletizable, and pelletizing the strand.

16. A molding composition obtained by the process as claimed in claim 13.

17. A pelletized material obtained by the process as claimed in claim 15.

18. A product, in particular a semifinished part or shaped part, obtained by extrusion or injection molding of the molding compositions as claimed in claim 16.

19. A method for producing products with relatively high flame resistance, the method comprising producing the products from the composition as claimed in claim 1 without additional flame retardants based on halogen-, nitrogen- or phosphorus-containing organic compounds or red phosphorus.

20. The method as claimed in claim 19, forming the products by extrusion or injection molding of the composition as claimed in claim 1.

Description

EXAMPLES

[0206] The components indicated in table 1 were mixed in a ZSK 26 Compounder twin-screw extruder from Coperion Werner & Pfleiderer (Stuttgart, Germany) at a temperature of about 280 C., discharged as strand into a water bath, cooled until pelletizable and pelletized. The pellets were dried to constant weight at 70 C. in a vacuum drying oven.

[0207] The pellets were subsequently processed on an Arburg A470 injection molding machine at melt temperatures in the range from 270 to 290 C. and tool temperatures in the range from 80 to 100 C. to give test specimens having a size of 80 mm10 mm4 mm and round plates having a diameter of 80 mm and a thickness of 0.75 mm, 1.5 mm or 3 mm.

[0208] The mechanical properties of the products produced from the compositions according to the invention were determined in a bending test in accordance with ISO 178 and in the IZOD impact test in accordance with ISO180/1U.

[0209] The glow wire resistance was determined by means of glow wire test GWFI (Glow Wire Flammability Index) in accordance with IEC 60695-2-12.

[0210] Good mechanical properties for the purposes of the present invention are indicated by, in particular, high values of the flexutral strength of products to be produced. The flexural strength in applied mechanics is a value of a flexural stress in a component subjected to bending, which when exceeded leads to failure by fracture of the component. It describes the resistance that a workpiece offers to deflection or fracture. In the short-term bending test in accordance with ISO 178, bar-shaped test specimens, preferably having the dimensions 80 mm10 mm4 mm, are placed at the ends on two supports and loaded in the middle by means of a bending punch (Bodo Carlowitz: Tabellarische bersicht ber die Prfung von Kunststoffen, 6th edition, Giesel-Verlag fr Publizitt, 1992, pp. 16-17).

[0211] In accordance with http://de.wikipedia.org/wiki/Biegeversuch, the flexural modulus is determined in a 3-point bending test by positioning a test specimen on two supports and loading it in the center with a test punch. This is probably the most commonly used form of bending test. The flexural modulus is then calculated in the case of a flat sample as follows:

[00001]$E=\frac{l_v^3\left(X_H-X_L\right)}{4.Math..Math.D_L.Math.{\mathrm{ba}}^3}$

[0212] where E=flexural modulus in kN/mm.sup.2; I.sub.v=support width in mm; X.sub.H=end of flexural modulus determination in kN; X.sub.L=start of flexural modulus determination in kN; D.sub.L=deflection in mm between X.sub.H and X.sub.L; b=sample width in mm; a=sample thickness in mm.

[0213] The edge fiber elongation can be determined from a thermal property of a material, viz. the heat distortion resistance. Heat distortion resistance is a measure of the thermal durability of plastics. Owing to the fact that they have viscoelastic behavior, there is no strictly defined upper use temperature for plastics; instead, a substitute parameter is determined under defined load. Two standardized methods are available for this purpose.

[0214] This method described in DIN EN ISO 75-1,-2,-3 (predecessor: DIN 53461) for determining the heat distortion resistance temperature (HDT=heat deflection temperature) uses standard test specimens which have a rectangular cross section and are preferably subjected on a flat side to three-point bending under constant load. Depending on the test specimen height, an edge fiber strain .sub.f of 1.80 (Method A), 0.45 (Method B) or 8.00 N/mm.sup.2 (Method C) is applied by using weights or/and springs to apply a force

[00002]$F=\frac{2.Math.{}_f.Math.{\mathrm{bh}}^2}{3.Math.L}$ [0215] b: Specimen width [0216] h: Specimen height [0217] L: Support spacing

[0218] The loaded specimens are subsequently subjected to heating at a constant heating rate of 120 K/h (or 50 K/h). If the deflection of the specimen reaches an edge fiber elongation of 0.2%, the corresponding temperature is the heat distortion resistance temperature (heat deflection temperature or heat distortion temperature) HDT. In the case of the method HDT-A which is frequently used, thus also for the purposes of the present invention, the applied flexural stress is 1.8 MPa.

[0219] The impact toughness in accordance with ISO 180/1U is a measure of the ability of a material to absorb impact energy and percussion energy without breaking. Here, many factors determine the impact strength of a component: [0220] wall thickness [0221] shape and size of the component [0222] temperature [0223] impact speed

[0224] The impact toughness is measured by means of an impact hammer. The impact toughness is calculated as the ratio of impact energy and test specimen cross section (unit of measurement: kJ/m.sup.2). There are various measurement methods, viz. the Charpy or IZOD methods. In the IZOD method used for the purposes of the present invention, the test specimen is clamped upright and only on one side.

[0225] The evaluation of the thermal stability, which is an important factor in determining the processing window, was carried out by means of thermogravimetric analysis (TGA). For this purpose, the specimen was heated in air in a TGA instrument (Netzsch TG209 F1 Iris) at a heating rate of 20.0 K/min and the change in mass over the temperature was recorded. The temperature at which a cumulated decrease in mass of 2% occurred was defined as the temperature T(Z) at which the thermal stability is no longer satisfactory.

[0226] Materials Used: [0227] Component a/1: Polyamide 6 (Durethan B29, from Lanxess Deutschland GmbH, Cologne, Germany) [0228] Component b/1: Kyanite, e.g. Silatherm-T 1360-400 AST from Quarzwerke GmbH, Frechen, Germany [0229] Component b/2: Magnesium hydroxide, e.g. Magnifin 5HIV, Martinswerk GmbH, Bergheim, Germany

[0230] Component f): Further additives customarily used in polyamides, for example mold release agents (in particular ethylenebis(stearylamide), [CAS-No. 110-30-5], nucleating agents (e.g. based on talc). Type and amount of the additives referred to collectively as component f) correspond in type and amount for the examples and comparative examples.

[0231] The compositions shown in Table 1 were all processed in the manner described above.

TABLE-US-00001 TABLE 1 Example using triclinic aluminum silicate without further flame retardant Ex.1 Comp. 1 a/1 [%] 24.69 24.69 b/1 [%] 75 b/2 [%] 75 f [%] 0.31 0.31 IZOD [kJ/m.sup.2] 23 10 Flexural strength [Mpa] 161 140 Edge fiber elongation [%] 1.9 1.1 GWFI (1.5 mm) at 750 C. passed passed GWFI (3 mm) at 960 C. passed passed Commencement of [ C.] 360 320 decomposition

[0232] Compositions according to the invention and products obtainable therefrom (Ex.1) thus display a very much higher decomposition temperature and thus a significantly wider processing window at a comparable glow wire performance compared to the variant using a flame retardant (here magnesium hydroxide) (Comp.1).

[0233] A GWFI of 750 C. meets, in accordance with IEC60335-1, the standardized requirements for use as insulating material for electric current-conducting parts at >0.5 A in domestic appliances subject to supervision. The use of aluminum silicate at the same filler content results in significantly better mechanical properties.