materials | Thermally conductive


Table 1: Mechanical and thermal properties of PA6 compounds containing different Silatherm aluminosilicate fi llers at 65 wt% loadings


Mechanical properties Filling Product


Silatherm 1360-400 AST Silatherm T 1360-400 AST


Silatherm Advance 1438-800 AST Thermal properties


Tensile stress


[wt.%] [MPa] 65 65 65


94 94


104 Filler proportion Product


Silatherm 1360-400 AST Silatherm T 1360-400 AST


Silatherm Advance 1438-800 AST


Target [wt.%]


65 65 65


*AC


[wt.%] 64,4 64,1 63,7


Density [g/cm³]


1,99 1,99 2,27


Breaking


3,7 4,2 6,2


[MPa] 10000 10100 8080


elongation E-Modulus resistance [%]


[kJ/m²] 42,1 61,5 95,2


Z-direction Thermal


HDT A cp conductivity [°C] [J/gK] [W/mK]


142 140 119


*Ash content 750°C; 10 min. (Thermal conductivity of unfi lled PA is 0.3 W/mK.)


applications for more than one year, according to the company’s Market Development Manager Péter Sebö. “Its use grants better properties regarding mechanical stiffness and thermal performance whilst being a perfect electrical insulator,” he says. One of the company’s most recent developments is Silatherm Advance, which Sebö describes as “a whole new grade of thermal conductive fi ller” that provides increased thermal conductivity and improved mechani- cal properties. The additive, like BN, is naturally white in colour. “Target application markets like EMC, automotive, LED-lightning systems and others are now within reach with this new product,” Sebö claims. Tests comparing the mechanical and thermal performance of Silatherm Advance 1438-800 AST in


1.08 1.09 0.93


1,2 1,0 1,0


0,92 0,69 0,87


Impact Notched impact resistance [kJ/m²]


3,1 4,3 5,9


X-direction Thermal


cp conductivity [J/gK] [W/mK]


1.3 1.3 1.4


Source: HPF The Mineral Engineers


polyamide 6 against with compounds using the company’s existing Silatherm 1360-400 AST and Silatherm T 1360-400 grades show positive results (see Table 1). “Silatherm Advance shows similar thermal conductivities, a much better impact and higher tensile stress,” says Sebö. “Higher fi ller proportions are possible to achieve higher thermal conductivities.” For example, at an addition rate of 75% (by weight) Silath- erm 1360-400 AST provides a thermal conductivity of 2.0 W/mK in PA6 ( the thermal conductivity of unfi lled PA is 0.3 W/mK).


Sebö also highlights the potential for combining Silatherm with BN as a route to obtaining cost-effective solutions for heat sinks and other applications. He says several investigations have been carried out, using similar conditions as in the previous experiments, but with a total concentration of 45% by volume (See Figure 2). A combination of the two fi llers enables a thermal conductivity up to 4.7 W/mK to be achieved, together with increased isotropy.


Imerys Graphite & Carbon says last year it observed an increasing interest for graphite-based products for thermally conductive plastics applications around the world. Graphite is the best option if electrical conductiv- ity is tolerated and high thermal conductivity is required in a plastic compound, according to Daniele Bonacchi, Development Scientist, R&D Polymer Applications with the company in Bodio, Switzerland.


Figure 2: Infl uence of aluminosilicate and born nitride combination blends on thermal conductivity and compound cost (based on a 45 volume% loading) Source: HPF The Mineral Engineers


50 INJECTION WORLD | May 2016


The main application Imerys is seeing for thermally conductive compound is, once again, LED heat sinks, especially for automotive applications. “According to the


www.injectionworld.com


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