Industrial minerals and functional fillers are broken down and carefully prepared, mostly from natural rocks typically found above ground and more rarely underground. This usually includes pre-sorting processes in which a targeted enrichment of the desired minerals and a reduction of the accessory minerals take place. The subsequent grinding steps guarantee uniform particle size distributions, which are absolutely essential to many purposes.
However, there is still a very long way to go before exhausting all the possibilities. With certain products, thermal processing steps or chemical deposition processes follow, which lead to modifications of the mineral structure or to an additional cleaning, and then ultimately to changed functionalities.
Certain natural, as well as some modified mineral products can then be selectively surface-treated in order to achieve improved bonding in the polymer matrix.
In this way, natural stones yield high-performance fillers which, thanks to their particle shape, size and structure, guarantee uniquely improved characteristics in polymers and elastomers, and often on very attractive terms. This is why we like to call them “functional fillers.”
The following products are particularly suitable for use in plastics and elastomers:
|Kaolin||Lamellar, natural and calcined types; delaminated, ultrafine to coarse, plastic, relatively soft (Mohs hardness 2-3), low abrasiveness; special coating available; light color||Uniform shrinkage behavior thanks to platelet shape, enhances mechanical properties such as toughness, elasticity and tensile strength|
|Mica||Lamellar, excellent elasticity, high heat resistance (up to approx. 550°C), excellent chemical resistance, light color, excellent electrical insulating properties; relatively soft (Mohs hardness 2-3), low abrasiveness||Uniform shrinkage behavior thanks to platelet shape, high heat deflection temperature, enhances mechanical properties such as toughness, elasticity, impact-resistance and tensile strength; excellent electrical insulating properties|
|Phlogopite mica||Lamellar, highly elastic, high heat resistance (up to approx. 800°C), excellent chemical resistance, excellent electrical insulating properties; relatively soft (Mohs hardness 2-3), low abrasiveness||Uniform shrinkage behavior thanks to platelet shape, high heat deflection temperature, enhances mechanical properties such as toughness, elasticity, impact-resistance and tensile strength; excellent electrical insulating properties|
|Talc||Lamellar, very soft (Mohs hardness 1), low abrasiveness, highly non-polar, light color||Talc is non-polar and is therefore ideal for use in polyolefins (particularly PP, but also PE); thanks to its platelet shape, it exhibits uniform shrinkage behavior and increases mechanical properties;is used as a nucleating agent (crystallization accelerator) in polyamides|
|Wollastonite||Needle-shaped, Mohs hardness 4.5; low thermal expansion coefficient; different qualities with high (needle-shaped) and low aspect ratio (block-shaped); surface treatment possible||High heat deflection temperature, enhances mechanical properties such as impact resistance and tensile strength; enhanced scratch resistance|
|Calcium carbonate, natural||Mohs hardness 3; natural variant of chalk (slightly less hard), limestone (high chemical purity) and marble (exceptionally white)||Inexpensive filler; for reduction of shrinkage and sink marks;|
|Precipitated calcium carbonate (PCC)||Mohs hardness 3; high purity and whiteness; even and fine particle structure achievable with specific measures||Functional filler; for enhancing surface shine; can be used as a TiO₂ extender|
|Micaceous iron oxide||Mohs hardness 6-6.5; platelet-shaped iron oxide (Fe2O3), chemically inert, metallic shine, high thermal conductivity||For increasing the thermal conductivity of polyolefin at low concentrations (3-5%); reduces cycle time of thick-walled components; coarser types can be used as a special effect pigment to achieve a metallic effect|
|Precipitated barium sulfate (Blanc Fixe)||Mohs hardness 3; regular and fine particle shape (~1µm); high density (4.8 g/cm3); light color; chemically inert;||For enhancing surface quality and shine; increasing density e.g. for reduction of noise or enhancing the texture|
|Glass beads||Mohs hardness 5-6; regular and smooth spherical shape; available in different sizes; various surface treatments available||For increasing mechanical values, reduction of shrinkage and anisotropy counteracts warping; enhances surface hardness and scratch resistance, as well as surface quality and shine|
Even at low concentrations of 3-5%, micaceous iron oxide can increase thermal conductivity by up to 50%. That is enough to reduce the cycle time of polyolefin in particular by up to 30% (with thick-walled components). Thanks to the low quantity needed, this has a minimal effect on the mechanical properties.
At the right concentration, thermal conductivity can be increased more than tenfold. To achieve the highest possible packing density, different qualities can be combined with different grain sizes. One key advantage is the retention of electrical insulating properties.