Electrically conducting thermally conductive polymer resin composition based on styrenics with balanced properties

Abstract

Thermally conductive polymer (TCP) resin compositions are described, comprising: 50 to 75% matrix polymer (I) comprising styrenic polymers () such as ABS (acrylonitrile-butadiene-styrene) resins, ASA (acrylonitrile-styrene-acrylate) resins and elastomeric block copolymers of the structure (S-(B/S)).sub.n-S; and 25 to 50% thermally conductive filler material (II) (D.sub.50 0.1 to 200 m), consisting of carbonyl iron powder (11-1) in mixture with multi wall carbon nanotubes, silicon carbide, diamond, graphite, aluminosilicates and/or boron nitride (II-2); wherein the volume ratio of (ll-1)/(ll-2) is 15:1 to 0.1:1. Shaped articles made thereof can be used for materials with antistatic finish, electrical and electronic housings, toys and helmet inlays.

Claims

1. A thermally conductive polymer (TCP) resin composition comprising components (I) and (II): 50 to 75% by volume of at least one matrix polymer (I), comprising at least one styrenic polymer (I) selected from the group consisting of: ABS (acrylonitrile-butadiene-styrene) resins, ASA (acrylonitrile-styrene-acrylate) resins, and elastomeric block copolymers of the structure (S-(B/S)).sub.n-S, 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 25 to 60% by weight of diene and 75 to 40% by weight 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., and the proportion of the hard phase in the elastomeric block copolymer is from 5 to 40% by weight and the relative amount of 1,2 linkages of the polydiene, based on the sum of 1,2- and 1,4-cis/trans-linkages, is less than 15%; 25 to 50% by volume of a thermally conductive filler material (II) having a weight median particle diameter (D.sub.50) of from 0.1 to 200 m, which consists of carbonyl iron powder as component (II-1) in mixture with at least one component (II-2) selected from the group consisting of: multi wall carbon nanotubes, silicon carbide, diamond, graphite, aluminosilicates and boron nitride; wherein the volume ratio between components (II-1) and (II-2) is from 15:1 to 0.1:1; and wherein the sum of components (I) and (II) totals 100% by volume.

2. The TCP resin composition according to claim 1, wherein the thermal conductivity is more than 0.5 W/m.Math.K.

3. The 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.

4. 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.

5. The TCP resin composition according to claim 1, comprising 57 to 70%, preferably 60 to 69%, by volume of component (I) and 30 to 43%, preferably 31 to 40%, by volume of component (II).

6. The TCP resin composition according to claim 1, wherein the volume ratio between components (II-1) and (II-2) is from 10:1 to 0.5:1, preferably 7:1 to 1:1, more preferred 5:1 to 2:1.

7. The TCP resin composition according to claim 1, wherein component (II-2) is graphite or multi wall carbon nanotubes.

8. The TCP resin composition according to claim 1, wherein the matrix polymer (I) consists of an elastomeric linear styrene-butadiene block copolymer of the general structure S-(B/S)-S having, situated between the two styrene S blocks, one (B/S)-random block having random styrene/butadiene distribution.

9. A process for the preparation of the TCP resin composition according to claim 1 by (i) melt-mixing of the matrix polymer (I) and (ii) addition and homogeneous dispersion of the filler material B) to the melt.

10. A shaped article comprising the TCP resin composition according to claim 1 formed by injection molding, extrusion, compression forming, vacuum forming, or blow molding.

11. A method of using a shaped article according to claim 10 for materials with antistatic finish, electrical and electronic housings, toys, and helmet inlays.

Description

EXAMPLES

(1) Materials:

(2) Component (I):

(3) Elastomeric block copolymer: Styroflex 2G 66 from Styrolution (Frankfurt, Germany), a linear styrene-butadiene triblock copolymer (SBC) of the structure S-(S/B)-S, the amount of the monomers in the total block copolymer is 35% by weight of butadiene and 65% by weight of styrene; the weight ratio of the blocks is 16/68/16; MFI: 14 (200 C./5 kg) g/10 min.

(4) Component (II):

(5) Carbonyl Iron Powder (CIP): spherical particles 3.0 to 5.0 m, coated with SiO.sub.2, density: 7.8 g/cm.sup.3 (source: BASF SE, Germany).

(6) MWNT: Multiwall (Carbon) Nanotubes, average diameter 9.5 nm, average length 1.5 m, density: 1.75 g/cm.sup.3, purity: 90% carbon (source: Nanocyl S. A., NC 7000MWCNT).

(7) Graphite: natural occurring graphite flakes, up to 325 mesh, density: 2.26 g/cm.sup.3, 99.8% purity (source: Alfa Aesar GmbH & Co KG, Germany).

(8) Boron nitride (BN): Mixed platelets, agglomerates, D.sub.50=16 m, density: 2.2 g/cm.sup.3 (Boron nitride CF600 from Momentive Performance Materials Inc., USA).

(9) Diamond: Single crystalline powder, D.sub.50=0.25 to 45 m, density: 3.52 g/cm.sup.3 (source: Schmitz-Metallographie GmbH, Germany).

(10) Silicon carbide: black modification, D.sub.50=30.5 m, density: 3.2 g/cm.sup.3 (source: Mineralienhandel Brgel, Germany).

(11) Aluminosilicate: Silatherm Grade: 1360-400 MST (source: Quarzwerke Frechen), a natural occurring aluminosilicate treated with methacrylsilane, D50=5 m (D10=1 m, D90=16 m), density: 3.65 g/cm.sup.3

(12) The TCP resin compositions were prepared by mixing and compounding matrix polymer (I) and filler material (II) with Haake Rheomix 600p (time: 30 min at 30 rpm, Temp. 220 C. for SBC, 240 C. for ABS, 250 C. Terblend N).

(13) Samples from the obtained TCP resin compositions were prepared by hot pressing with a Carver compression molding machine 25-12-2HC.

(14) Procedure for sample preparation for measurement of the thermal conductivity with Carver heated press 25-12-2HC

(15) Compound lumps of the TCP resin compositions obtained from the kneader Haake Rheomix 600p are placed in the middle of a sandwich consisting of a metal plate, a release foil (e.g. glass fabric enhanced PTFE), a metal spacer (1 mm thickness) for adjusting the thickness of the resultant sample, again a release foil and a metal plate.

(16) This sandwich is preheated in the Carver heated press 25-12-2HC (220-250 C. depending on utilized polymer) without applied pressure for 2 min to 4 min (depending on the time needed for softening of the respective compound).

(17) After the material has softened a pressure of 6 metric tons is applied to the sandwich for 1 min. Afterwards the sandwich is removed and placed in a water cooled press for re-cooling with an applied force of 8 kN. Finally a 1 mm thick sample piece is received for investigation of the thermal conductivity.

(18) Procedure for Sample Preparation for Measurement of the Electrical Bulk Resistivity

(19) Compound lumps of the TCP resin compositions obtained from the kneader Haake Rheomix 600p were granulated. Afterwards the granulate material was processed with a DSM Xplore Micro Injection molder and a mold giving universal test specimen with 80 mm*10 mm*4 mm size. Therefore a melt temperature of 260 C., a mold temperature of 50 C. and an injection pressure of 16 bar for 22 s were applied.

(20) Measurement Methods:

(21) 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) electrical bulk resistivity was measured according to DIN EN ISO 3915 3 universal test specimens 80 mm10 mm4 mm per material electrodes are applied at both sides of the test bar by silver paint sample was preconditioned at 60 C. for 5 hrs, then stored for 16 hrs at 23 (+/2) C. and 50 (+/5) % relative humidity application to sample holder, application of constant current (1 mA), potential measured on front and back side of the sample distance between measurement electrodes (10 mm) deviation from ISO standard: measurement was not orthogonal to injection direction, instead measurements of front and backside calculation formula for electrical resistivity: =U*A/(I*d)

(22) Table 1 shows inventive TCP resin compositions with a filler material (II)a mixture of CIP (II-1) and a further thermally conductive filler material (II-2)in Styroflex 2G66 as matrix polymer (I). The sum of components (I) and (II) totals 100% by volume.

(23) TABLE-US-00001 TABLE 1 Matrix (I): Styroflex 2G66, Filler material (II-1): CIP total Additive Volume Filler Thermal Heat Thermal Electrical (II) Ratio material diffusivity Density capacity conductivity Resistivity Exp. No. vol % (II-1)/(II-2) (II-2) cm.sup.2/s g/cm.sup.3 J/g*K W/m*K Ohm*m Cp. Exp. 1 33.3 0.00208 3.33 0.693 0.481 1 33.3 10:1 MWNT 0.00296 3.123 0.719 0.664 2 33.3 5:1 MWNT 0.00351 3.002 0.699 0.736 2.00 3 33.3 10:1 SiC 0.00257 3.156 0.698 0.567 4 33.3 10:1 Graphite 0.00255 3.123 0.67 0.533 5 33.3 5:1 Graphite 0.00275 2.978 0.663 0.543 6 33.3 2.5:1.sup. Graphite 0.003523 2.7767 0.744 0.728 7 33.3 5:1 BN 0.002955 2.9733 0.695 0.61 8 33.3 3:1 alumino- 0.00273 2.860 0.732 0.57 silicate

(24) The data in Table 1 show that the further thermally conductive filler component (II-2) acts synergistically with the CIP (I-1). All mixtures from Table 1 have the same total filler content; comparative example 1 contains no further thermally conductive filler component (II-2). By exchanging a defined portion of CIP with a further thermally conductive filler (II-2) the thermal conductivity of the resulting resin composition can be enhanced by 7 to 30%.

(25) Mechanical Characterization

(26) Larger amounts for mechanical characterization of mixture from example 8 have been produced with Coperion twin-screw extruder ZSK26Mcc (D=26 mm, L/D=44) using feed enhancement technology (FET) (melt temperature: 246 C., total throughput: 30 kg/h, melt pressure: 16 bar, screw speed: 350 1/min, temperature (zones 1 to 12): 220 C.).

(27) Injection molding of dog bones (170 mm*10 mm*4 mm) and Charpy samples (80 mm*10 mm*3 mm) with Arburg 320 S Allrounder 500-150 (T(melt): 220 C.; T(mold): 50 C.). notched Charpy impact strength was determined according to ISO 179/1eA (sample preparation with Circular Saw Mutronic Diadisc 6200 and V-notch saw blade) un-notched Charpy impact strength was determined according to ISO 179/1eU Impact pendulum Zwick/Roell RKP 5113 (50 J hammer)

(28) Tensile test: E-modulus was determined according to DIN EN ISO 527 Test of tensile properties with Universal testing machine Zwick Z020 with macro displacement transducer (speed for tensile modulus: 1 mm/min; rest of test: 50 mm/min).

(29) Flow curve and shrinkage evaluation Instrument: Rheograph 6000 (Gttfert) Measurement parameters: Temperature selected based on polymer: Styroflex 2G66 (200 C.) Procedure a) Measurement of the flow curve. This gives the actual shear rate for the utilized dye geometry (30 mm length, 1 mm diameter) and the selected two piston speeds during the melt density measurements. b) Measurement of the melt density: The column of the capillary rheometer is filled with the respective material, compressed by the stamp followed by a temperature equilibration. Afterwards the material is extruded through the die with the respective piston speeds. During the extrusion several material samples extruded between different fill levels are collected. With the known extruded fill level height and the column diameter the extruded volume is known. Together with the weight of the extruded sample the density in the molten state under the respective actual shear in the column is received.

(30) $\mathrm{Calculation}\mathrm{of}\mathrm{Shrinkage}:\mathrm{Shrinkage}\left[\frac{}{}\right]=\frac{\mathrm{density}\left(\mathrm{RT}\right)-\mathrm{density}\left(\mathrm{melt}\right)}{\mathrm{density}\left(\mathrm{RT}\right)}*100\%$

(31) The Melt Volume Rate (MVR) was measured according to DIN EN ISO 1133-1:2012-03.

(32) TABLE-US-00002 TABLE 2 Mechanical Properties and Shrinkage Charpy Charpy un- Tensile MVR Exp. notched notched modulus Shrinkage (200/21.6) No. [kJ/m.sup.2] [kJ/m.sup.2] [MPa] [%] [ml/10 min] 8 47.2 no 135 2.9 27.70 break

(33) Results:

(34) From mechanical characterization in table 2 it becomes clear that according to the invention TCPs with high toughness are obtained; measurement of un-notched Charpy shows no break and notched Charpy yields a high value. In addition high melt flow and low shrinkage are very beneficial for injection molding applications.