Resistivity migration

The following factors, in combination with the plastic to be colored, are decisive in determining the suitability of a colorant for a particular application namre, thermal load capacity (level and duration), light fastness, weather resistance, migration tendency (solvent and cmitact bleeding, blooming), plateout (deposits on metal surfaces in contact with melt) and influence on flow behavior [45]. 

The most common simple phenolic is butylated hydroxytoluene (BHT) or 2,6-di-t-butyl-4-methylphenol. BHT possesses broad FDA approval and is widely used as an antioxidant in a variety of polymers. It is commonly called the workhorse of the industry but is losing ground to the higher molecular weight antioxidants which resist migration. The disadvantage of BHT is that it is highly volatile and can cause discoloration. Other simple phenolics include BHA (2- and 3-t-butyl-4-hydroxyanisole) which is frequently used in food applications. 

There is a growing demand for Tow smoke zero halogen compositions in wire and cable. In 2002, such grades amounted to 15% of all the polyethylene cable compounds used in Western Europe. Antioxidants and metal deactivators are used to protect the insulation against copper compoimds that can otherwise promote failure in polyolefins. The additives need to withstand prolonged heat and to resist migration and decomposition. 

The Flamingo stent was designed specifically to resist migration. The migration resistant features of this stent have been described above. In a small pilot study involving ten patients with strictures in the lower esophagus, distal migration of these stents did... 

The main criteria that are used to classify pigments as HPOPs are heat stability, lightfastness, weather fastness, durability, solvent resistance, migration resistance, color strength, dispersibility and value in use. Improvements in some of these areas are still required for many HPOPs. 

As mentioned in the discussion of dielectric loss, the presence of porosity in dielectric materials can lower the insulation resistance because of absorption of moisture and crystalline defects at the surfaces of pores. The migration of electrode material into the dielectric during firing can lower the insulation resistance. Migration of metals or other conducting ions through interconnected porosity in a humid atmosphere can also cause loss of insulation resistance. 

Hitco calcium stearates can also reduce the possibility of "bloom," and the resultant color distortion, because they resist migration to the surface of finished products during storage. 

Ceiresien Resistance. Migration of water to adhesive joints is the most common form of bond degradation. Figure 7 conqrares the loss of strength in aluminum-epoxy joints after exposure in a hot-wet environment with the excellent durability that can be achieved under dry conditions. 

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