Thermally conductive polymer resin composition based on styrenics with low density

Abstract

Thermally conductive polymer (TCP) resin compositions are described, comprising components (X) and (Y): 90 to 99.9% component (X) comprising components (I) and (II): 60 to 85% matrix polymer (I) comprising styrenic polymers (F) selected from: ABS resins, ASA resins, and elastomeric block copolymers of the structure (S(B/S)).sub.nS; 15 to 40% thermally conductive filler material (II) (D.sub.50 1 to 200 ), consisting of a ceramic material and/or graphite; 0.1 to 10% chemical foaming agent (Y). Shaped articles made thereof can be used for automotive applications, as a heat sink for high performance electronics, LED sockets or electrical and electronic housings.

Claims

1. A thermally conductive polymer (TCP) resin composition comprising components (X) and (Y): 90 to 99.9% by weight of component (X) which is a composition comprising components (I) and (II): 60 to 85% by volume of at least one matrix polymer (I) as component (I) comprising styrenic polymers (I) selected from the group consisting of: ABS (acrylonitrile-butadiene-styrene) resins, ASA (acrylonitrile-styrene-acrylate) resins, and elastomeric block copolymers; wherein the elastomeric block copolymers have a structure
(S(B/S)).sub.nS, where S is a vinylaromatic block forming a hard phase, (B/S) is a random copolymer block of vinylaromatic monomer and of a conjugated diene forming a soft phase, and n are natural numbers from 1 to 10, wherein the elastomeric block copolymer has a monomer composition comprising from 25 to 60% by weight (based on the elastomeric block copolymer) of diene and from 75 to 40% by weight (based on the elastomeric block copolymer) of vinylaromatic compound, the glass transition temperature Tg of block S is above 25 C. and that of block (B/S) is below 25 C., wherein the proportions of the soft phase and the hard phase total 100% by weight and the proportion of the hard phase in the elastomeric block copolymers is from 5 to 40% by weight and the relative amount of 1,2 linkages of the diene, based on the sum of 1,2- and 1,4-cis/trans-linkages, is less than 15%; 15 to 40% by volume of at least one thermally conductive filler material (II) as component (II) having a weight median particle diameter (D.sub.50) of from 1 to 200 m, which consists of at least one ceramic material and/or graphite; wherein components (I) and (II) total 100% by volume; 0.1 to 10% by weight of at least one chemical foaming agent as component (Y); wherein components (X) and (Y) total 100% by weight; and the thermal conductivity K is more than 0.4 W/mK.

2. The thermally conductive polymer (TCP) resin composition according to claim 1, wherein the matrix polymer (I) comprises at least one further thermoplastic polymer (I) selected from the group consisting of: polycarbonates and polyamides.

3. The TCP resin composition according to claim 1, wherein the matrix polymer (I) is selected from the group consisting of: ABS resins, ASA resins, elastomeric block copolymers of the structure (A-(B/A)).sub.n-A, blend of ABS resins with polycarbonate, blend of ABS resins with polyamide, blend of ASA resins with polycarbonate, and blend of ASA resins with polyamide.

4. The TCP resin composition according to claim 1, wherein component (X) comprises 65 to 80% by volume of component (I) and 20 to 35% by volume of component (II).

5. The TCP resin composition according to claim 1, comprising 95 to 99.5% by weight of component (X) and 0.5 to 5% of component (Y).

6. The TCP resin composition according to claim 1, wherein the thermally conductive filler material (II) consists of boron nitride, aluminosilicate, and/or graphite.

7. The TCP resin composition according to claim 1, wherein the chemical foaming agent is at least one compound selected from the group consisting of: Sodium carbonate, Sodium hydrogen carbonate, Magnesium carbonate, Stearic acid, Sodium stearate, Potassium stearate, Magnesium stearate, Zinc carbonate, and Citric acid derivatives.

8. The TCP resin composition according to claim 1, wherein the thermally conductive filler material (II) is boron nitride.

9. The TCP resin composition according to claim 1, wherein the thermally conductive filler material (II) is a mixture of boron nitride (II-1) and aluminosilicate (II-2).

10. The TCP resin composition according to claim 1, wherein the matrix polymer (I) is an ABS resin.

11. The TCP resin composition according to claim 1, wherein the elastomeric block copolymer (I) is a linear styrene-butadiene block copolymer of the general structure S(B/S)S having, situated between the two styrene S blocks, one or more (B/S)-random blocks having random styrene/butadiene distribution.

Description

EXAMPLES

(1) Materials:

(2) Component I:

(3) ABS: Terluran HI-10 (high impact, medium flow, injection molding and extrusion grade ABS of Styrolution, Frankfurt).

(4) Elastomeric block copolymer: Styroflex 2G 66 from Styrolution, Frankfurt.

(5) Component II:

(6) Boron nitride (BN-1): hexagonal crystal structure, plates, D.sub.50=7 m, D.sub.100=30 m, density: 2.2 g/cm.sup.3 (Boron nitride PCTFS from Saint Gobain, Germany).

(7) Boron nitride (BN-2): Mixed platelets, agglomerates, D.sub.50=16 m, density: 2.2 g/cm.sup.3 (Boron nitride BN CFX1022 from Momentive Performance Materials Inc., USA).

(8) Aluminosilicate: Silatherm Grade: 1360-400 MST (source: Quarzwerke Frechen), a natural occuring aluminosilicate treated with methacrylsilane, D.sub.50=5 m (D.sub.10=1 m, D.sub.90=16 m), density: 3.65 g/cm.sup.3.

(9) Component Y:

(10) CFA: Hydrocerol 473 from Clariant Masterbatches (Deutschland) GmbH.

(11) Matrix polymer (I) and filler material (II) were mixed and compounded with a twin screw extruder ZSK 26 from Coperion GmbH (length/diameter (L/D)-ratio: 40). The obtained homogeneous polymer composition was then formed into granulate.

(12) Then the foaming agent (Y) (2 wt.-%, based on the entire composition consisting of components (I), (II) and (Y)) was pre-mixed to said granulate and processed by injection molding (machine: Arburg 320 S500-150):

Examples 1 and 2, Comparative Examples 1 and 2

(13) Sample plates: 80 mm*80 mm*2 mm (one side polished) processing conditions: T(cylinder)=260 C., T(mold)=70 C., injection speed 170 cm.sup.3/s, max. injection pressure 1000 bar, packing pressure 0 bar

(14) Measurement Methods:

(15) Thermal conductivity =.Math.c.sub.p.Math.: thermal diffusivity : determined by Laser flash analysis (XFA 500 XenonFlash apparatus (Linseis) with an InSb infrared detector) through-plane measurement, Temp. 25 C. under air specific heat c.sub.p was determined by DSC (TA Instruments Q1000 DSC), 20 K/min, 50 ml/min N2, 10 to 30 mg sample, ASTM E1269 temperature program: 1. slope set to 200 to 215 C. 2. isotherm for 10 minutes 3. slope set to minus 40 C. 4. isotherm for 10 minutes 5. slope set to 200 to 215 C. density is determined by Buoyancy Balance (Mettler Toledo AG245)

(16) Mechanical Characterization Injection molding of Charpy samples (80 mm*10 mm*3 mm) with Engel e-mac 50 (Table 3) un-notched Charpy impact strength was measured according to ISO 179/1eU

(17) Table 1 shows the results of the inventive foamed TCP ABS resin compositions (Exp. 1 and 2) comprising boron nitride (BN-1) and a CFA in comparison to a compact TCP ABS resin composition (cp. Exp. 1 and 2) prepared without CFA. The amount of the filler material in % by weight is based on the total of components (I) and (II).

(18) TABLE-US-00001 TABLE 1 wt.-% Thermal Thermal Sample BN Vol.-% BN diffusivity conductivity No. (II) (II) [cm.sup.2/s] [W/m .Math. K] cp. Exp. 1 40 23.3 Compact 0.002455 0.352 Exp. 1 Foamed 0.00277 0.432 cp. Exp. 2 50 31.3 Compact 0.00412 0.635 Exp. 2 Foamed 0.005495 0.901

(19) Table 1 shows that the thermal diffusivity is significantly increased by chemical foaming depending on the filler level (40 wt-%: 11%, 50 wt-%: 42%). A significant increase of the thermal conductivity can be also established. Compared at the same filler content by volume, the foamed resin composition has a significantly higher thermal conductivity than the not foamed resin composition.

Example 3

(20) TABLE-US-00002 TABLE 2 TCP resin composition Component (I) Component (II-1) Component (II-2) Additive (Z) 60 vol. % 36.4 vol.-% BN-2 3.6 vol.-% 2 wt.-% TiO.sub.2 Styroflex (64.7 wt.-%) aluminosilicate, (based on 2G66 (6.0 wt.-%) entire resin composition)

(21) As described for examples 1 and 2 above a granulate was obtained from the composition as shown in Table 2 above. The foaming agent (Y) (2 wt.-%, based on the entire composition consisting of components (I), (II), (Z) and (Y)) was pre-mixed to said granulate and processed by injection molding (machine: Engel e-mac 50, screw diameter 30 mm, plates: 70 mm*70 mm*4 mm) under the following conditions: T(cylinder) 220 C., T(mold) 50 C., injection speed 75 cm.sup.3/s, melt pressure 100 bar, packing pressure 100 bar/0.1 s, weight reduction 5.10%, cooling time 25 s

(22) Said sample plates (70 mm*70 mm*4 mm) were used to determine the thermal conductivity. For the measurement of the un-notched Charpy impact strength un-notched Charpy impact strength was determined according to ISO 179/1 eU foamed universal test specimens (plates: 80 mm*10 mm*3 mm) have been prepared under the injection molding conditions as hereinbefore mentioned, but the cooling time is 20 s.

(23) Compact universal test specimens (comparative examples, without foaming agent) for comparative measurements have been prepared under the same conditions as hereinbefore mentioned.

(24) The results of the measurements of example 3 (foamed) and comparative example 3 (compact) are shown in Tables 3 and 4.

(25) TABLE-US-00003 TABLE 3 Thermal conductivity Kappa [W/m*K] Increase in thermal Thermal diffusivity [cm.sup.2/s] Heat capacity [J/g*K] Compact Foamed* conductivity Compact Foamed* Compact Foamed 3 0.991 1.133 14.33% 0.00486 0.00579 0.936 0.936 (*measured at end of flow path)

(26) TABLE-US-00004 TABLE 4 Mechanical properties: Un-notched Charpy impact strength Weight [kJ/m.sup.2] reduction Compact foamed [%] 3 46.46 56.48 5.1

(27) The obtained data show a strong increase in the thermal conductivity and a weight reduction of 5.1% is observed. The un-notched Charpy impact strength is not deteriorated by foaming.