TABLE OF CONTENTS The main market for antiblocks continues to be thin-gauge packaging film. When antiblocks are incorporated to correct blocking there is a loss of clarity, gloss and haze. Agricultural film does not require ultrahigh clarity, but it needs to be clear enough to allow visual inspection of the plants. The same principle applies to the packaging of goods on retail display.
Antiblock suppliers have therefore been concerned in recent years with achieving the best overall balance of properties, including haze, yellowness and coefficient of friction. Both slip and antiblocking additives tend to lower the permeability of the film towards oxygen, carbon dioxide and water vapour.
Two trends have made a good balance of antiblocking, friction and optical properties more difficult to achieve:
There is a strong demand for ultraclear polyolefin film (such as LLDPE-octene copolymers) for packaging. The high optical quality specified is a difficult challenge to formulators.
The newer metallocene LLDPEs require a high antiblock dose level, and the adverse effects on haze and other properties increase with an increase in the antiblock dose level.
In addition, some Asian and Middle Eastern countries are using a water-quenched process for the conversion of PP tubular film, most of which needs good optical properties. The film tube has to be opened up by hand immediately after conversion, and this requires good antiblocking properties to prevent delays through sticking.
Sibelco is marketing Minbloc, a cristobalite powder with no coarse particles and a particle size distribution that gives excellent...
