TABLE OF CONTENTS For most PVC-U and PVC-P applications, fillers are added primarily to reduce formulation cost, but some are also used to enhance properties and performance. There is a balance between the cost benefits and any acceptable deterioration in physical properties that could result. The density of the final product will increase, of course, at higher filler levels.
Another important aspect is the influence on processing with respect to output, plate-out, and surface finish.
Calcium carbonate (also known as chalk) is the most commonly used filler for PVC. This material is mined as calcite mineral, milled, and classified to a particular particle size range. Surface treatment with stearic acid can be carried out with the stearic acid converting to calcium stearate in the process. This results in improved processing and dispersion (mechanical properties) and improved moisture resistance giving better electrical properties.
Synthetically precipitated calcium carbonates (PCC) are manufactured from the natural material by calcination, hydration, recarbonation, and precipitation from solution to give a fine particle size suitable for use in high-performance areas. Surface treatment is also normal.
Particle size is important and, for some applications requiring good weathering and impact performance (window profiles), the ultrafine milled, high whiteness, natural version is normally used. Coated ultrafi ne and precipitated calcium carbonates are also claimed to have a positive effect on impact properties in impact-modified formulations. The abrasive wear of calcium carbonate on melt processing equipment is not considered significant but increases with increasing levels.
Chalk fillers...
