Blister disc

Restrictive discs and blister discs restrict the melt flow over the entire cross-section of the barrel bore. Blister discs (Fig. 12.35) are drilled cylinder discs arranged concentrically around the screw shaft with a defined gap with respect to the barrel wall. A ring is fitted to the counter shaft similar to the TME element. This blocks the entire cross-section of the... 

Cargill Dow has some commercial applications in Europe and Asia. A major market has been blister packaging used to wrap such products as Sony Walkman radios and digital versatile discs (DVDs). 

Studies of blistering (acantholysis and vesiculation) show that disc proteins are attacked by papain, trypsin, and by reagents that split sulfur or hydrogen bonds (36, 37). Desmosomes and cells are also separated by extraction of calcium ions (35, 37), presumably from proteoglycans. Desmosomes are completely dissolved in vitro by chloroform methanol mixtures (38) that dissolve proteolipids (39). The separated cells become reaggregated after evaporation of the solvent leaving an intercellular deposit with normal appearance by electron microscopy (38). 

Figure 9.47 Dispersion of Ventodisk or Becodisk contents by breath actuation a cross-section of a Diskhaler is shown with a disc located on the support wheel, (a) A disc is located beneath an aperture in the body of the Diskhaler through which a piercing needle enters, (b) The needle penetrates the upper and lower surfaces of the blister, (c) The patient inhales through the device and pierced blister, entraining the blister contents into the airstream.

The blister test has also been used to study mould adhesion. It requires a special mould, but could probably be used with any moulding machine. It is well suited to measuring the low levels of adhesion involved in mould release. Essentially a disc, like a beer mat, is moulded and the pressure is applied to displace it through a small hole ( penny-shaped crack ) at its centre. The detachment pressure can be related to the fracture energy. 

The BYK 310 additive is used to reduce surface tension to aid substrate wetting and to counter the effects of atomization from the disc which can often give rise to air entrapment that results in a paint film that is full of micro bubbles of air. The trapped bubbles rupture on stoving resulting in a blistered film. The BYK 310 assists these bubbles to burst before all solvents have flashed off. 

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